diff --git a/docs/sphinx/conf.py b/docs/sphinx/conf.py
index 15c19834fc..0b15bd8912 100644
--- a/docs/sphinx/conf.py
+++ b/docs/sphinx/conf.py
@@ -50,7 +50,7 @@ master_doc = 'index'
 
 # General information about the project.
 project = u'Synapse'
-copyright = u'2014, TNG'
+copyright = u'Copyright 2014-2017 OpenMarket Ltd, 2017 Vector Creations Ltd, 2017 New Vector Ltd'
 
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the
diff --git a/synapse/config/_base.py b/synapse/config/_base.py
index 1ab5593c6e..fa105bce72 100644
--- a/synapse/config/_base.py
+++ b/synapse/config/_base.py
@@ -81,22 +81,38 @@ class Config(object):
     def abspath(file_path):
         return os.path.abspath(file_path) if file_path else file_path
 
+    @classmethod
+    def path_exists(cls, file_path):
+        """Check if a file exists
+
+        Unlike os.path.exists, this throws an exception if there is an error
+        checking if the file exists (for example, if there is a perms error on
+        the parent dir).
+
+        Returns:
+            bool: True if the file exists; False if not.
+        """
+        try:
+            os.stat(file_path)
+            return True
+        except OSError as e:
+            if e.errno != errno.ENOENT:
+                raise e
+            return False
+
     @classmethod
     def check_file(cls, file_path, config_name):
         if file_path is None:
             raise ConfigError(
                 "Missing config for %s."
-                " You must specify a path for the config file. You can "
-                "do this with the -c or --config-path option. "
-                "Adding --generate-config along with --server-name "
-                "<server name> will generate a config file at the given path."
                 % (config_name,)
             )
-        if not os.path.exists(file_path):
+        try:
+            os.stat(file_path)
+        except OSError as e:
             raise ConfigError(
-                "File %s config for %s doesn't exist."
-                " Try running again with --generate-config"
-                % (file_path, config_name,)
+                "Error accessing file '%s' (config for %s): %s"
+                % (file_path, config_name, e.strerror)
             )
         return cls.abspath(file_path)
 
@@ -248,7 +264,7 @@ class Config(object):
                     " -c CONFIG-FILE\""
                 )
             (config_path,) = config_files
-            if not os.path.exists(config_path):
+            if not cls.path_exists(config_path):
                 if config_args.keys_directory:
                     config_dir_path = config_args.keys_directory
                 else:
@@ -261,7 +277,7 @@ class Config(object):
                         "Must specify a server_name to a generate config for."
                         " Pass -H server.name."
                     )
-                if not os.path.exists(config_dir_path):
+                if not cls.path_exists(config_dir_path):
                     os.makedirs(config_dir_path)
                 with open(config_path, "wb") as config_file:
                     config_bytes, config = obj.generate_config(
diff --git a/synapse/config/key.py b/synapse/config/key.py
index 6ee643793e..4b8fc063d0 100644
--- a/synapse/config/key.py
+++ b/synapse/config/key.py
@@ -118,10 +118,9 @@ class KeyConfig(Config):
         signing_keys = self.read_file(signing_key_path, "signing_key")
         try:
             return read_signing_keys(signing_keys.splitlines(True))
-        except Exception:
+        except Exception as e:
             raise ConfigError(
-                "Error reading signing_key."
-                " Try running again with --generate-config"
+                "Error reading signing_key: %s" % (str(e))
             )
 
     def read_old_signing_keys(self, old_signing_keys):
@@ -141,7 +140,8 @@ class KeyConfig(Config):
 
     def generate_files(self, config):
         signing_key_path = config["signing_key_path"]
-        if not os.path.exists(signing_key_path):
+
+        if not self.path_exists(signing_key_path):
             with open(signing_key_path, "w") as signing_key_file:
                 key_id = "a_" + random_string(4)
                 write_signing_keys(
diff --git a/synapse/config/registration.py b/synapse/config/registration.py
index f7e03c4cde..ef917fc9f2 100644
--- a/synapse/config/registration.py
+++ b/synapse/config/registration.py
@@ -41,6 +41,8 @@ class RegistrationConfig(Config):
             self.allow_guest_access and config.get("invite_3pid_guest", False)
         )
 
+        self.auto_join_rooms = config.get("auto_join_rooms", [])
+
     def default_config(self, **kwargs):
         registration_shared_secret = random_string_with_symbols(50)
 
@@ -70,6 +72,11 @@ class RegistrationConfig(Config):
             - matrix.org
             - vector.im
             - riot.im
+
+        # Users who register on this homeserver will automatically be joined
+        # to these rooms
+        #auto_join_rooms:
+        #    - "#example:example.com"
         """ % locals()
 
     def add_arguments(self, parser):
diff --git a/synapse/config/repository.py b/synapse/config/repository.py
index 2c6f57168e..6baa474931 100644
--- a/synapse/config/repository.py
+++ b/synapse/config/repository.py
@@ -70,7 +70,19 @@ class ContentRepositoryConfig(Config):
         self.max_upload_size = self.parse_size(config["max_upload_size"])
         self.max_image_pixels = self.parse_size(config["max_image_pixels"])
         self.max_spider_size = self.parse_size(config["max_spider_size"])
+
         self.media_store_path = self.ensure_directory(config["media_store_path"])
+
+        self.backup_media_store_path = config.get("backup_media_store_path")
+        if self.backup_media_store_path:
+            self.backup_media_store_path = self.ensure_directory(
+                self.backup_media_store_path
+            )
+
+        self.synchronous_backup_media_store = config.get(
+            "synchronous_backup_media_store", False
+        )
+
         self.uploads_path = self.ensure_directory(config["uploads_path"])
         self.dynamic_thumbnails = config["dynamic_thumbnails"]
         self.thumbnail_requirements = parse_thumbnail_requirements(
@@ -115,6 +127,14 @@ class ContentRepositoryConfig(Config):
         # Directory where uploaded images and attachments are stored.
         media_store_path: "%(media_store)s"
 
+        # A secondary directory where uploaded images and attachments are
+        # stored as a backup.
+        # backup_media_store_path: "%(media_store)s"
+
+        # Whether to wait for successful write to backup media store before
+        # returning successfully.
+        # synchronous_backup_media_store: false
+
         # Directory where in-progress uploads are stored.
         uploads_path: "%(uploads_path)s"
 
diff --git a/synapse/config/tls.py b/synapse/config/tls.py
index e081840a83..247f18f454 100644
--- a/synapse/config/tls.py
+++ b/synapse/config/tls.py
@@ -126,7 +126,7 @@ class TlsConfig(Config):
         tls_private_key_path = config["tls_private_key_path"]
         tls_dh_params_path = config["tls_dh_params_path"]
 
-        if not os.path.exists(tls_private_key_path):
+        if not self.path_exists(tls_private_key_path):
             with open(tls_private_key_path, "w") as private_key_file:
                 tls_private_key = crypto.PKey()
                 tls_private_key.generate_key(crypto.TYPE_RSA, 2048)
@@ -141,7 +141,7 @@ class TlsConfig(Config):
                     crypto.FILETYPE_PEM, private_key_pem
                 )
 
-        if not os.path.exists(tls_certificate_path):
+        if not self.path_exists(tls_certificate_path):
             with open(tls_certificate_path, "w") as certificate_file:
                 cert = crypto.X509()
                 subject = cert.get_subject()
@@ -159,7 +159,7 @@ class TlsConfig(Config):
 
                 certificate_file.write(cert_pem)
 
-        if not os.path.exists(tls_dh_params_path):
+        if not self.path_exists(tls_dh_params_path):
             if GENERATE_DH_PARAMS:
                 subprocess.check_call([
                     "openssl", "dhparam",
diff --git a/synapse/event_auth.py b/synapse/event_auth.py
index 4096c606f1..9e746a28bf 100644
--- a/synapse/event_auth.py
+++ b/synapse/event_auth.py
@@ -470,14 +470,14 @@ def _check_power_levels(event, auth_events):
         ("invite", None),
     ]
 
-    old_list = current_state.content.get("users")
+    old_list = current_state.content.get("users", {})
     for user in set(old_list.keys() + user_list.keys()):
         levels_to_check.append(
             (user, "users")
         )
 
-    old_list = current_state.content.get("events")
-    new_list = event.content.get("events")
+    old_list = current_state.content.get("events", {})
+    new_list = event.content.get("events", {})
     for ev_id in set(old_list.keys() + new_list.keys()):
         levels_to_check.append(
             (ev_id, "events")
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index a8034bddc6..e15228e70b 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -192,7 +192,6 @@ class FederationServer(FederationBase):
                     pdu_results[event_id] = {}
                 except FederationError as e:
                     logger.warn("Error handling PDU %s: %s", event_id, e)
-                    self.send_failure(e, transaction.origin)
                     pdu_results[event_id] = {"error": str(e)}
                 except Exception as e:
                     pdu_results[event_id] = {"error": str(e)}
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index f96561c1fe..125d8f3598 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -550,6 +550,19 @@ class TransportLayerClient(object):
             ignore_backoff=True,
         )
 
+    @log_function
+    def get_invited_users_in_group(self, destination, group_id, requester_user_id):
+        """Get users that have been invited to a group
+        """
+        path = PREFIX + "/groups/%s/invited_users" % (group_id,)
+
+        return self.client.get_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            ignore_backoff=True,
+        )
+
     @log_function
     def accept_group_invite(self, destination, group_id, user_id, content):
         """Accept a group invite
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index c7565e0737..09b97138c3 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -721,6 +721,24 @@ class FederationGroupsUsersServlet(BaseFederationServlet):
         defer.returnValue((200, new_content))
 
 
+class FederationGroupsInvitedUsersServlet(BaseFederationServlet):
+    """Get the users that have been invited to a group
+    """
+    PATH = "/groups/(?P<group_id>[^/]*)/invited_users$"
+
+    @defer.inlineCallbacks
+    def on_GET(self, origin, content, query, group_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        new_content = yield self.handler.get_invited_users_in_group(
+            group_id, requester_user_id
+        )
+
+        defer.returnValue((200, new_content))
+
+
 class FederationGroupsInviteServlet(BaseFederationServlet):
     """Ask a group server to invite someone to the group
     """
@@ -817,7 +835,7 @@ class FederationGroupsRenewAttestaionServlet(BaseFederationServlet):
     def on_POST(self, origin, content, query, group_id, user_id):
         # We don't need to check auth here as we check the attestation signatures
 
-        new_content = yield self.handler.on_renew_group_attestation(
+        new_content = yield self.handler.on_renew_attestation(
             origin, content, group_id, user_id
         )
 
@@ -1109,12 +1127,12 @@ ROOM_LIST_CLASSES = (
     PublicRoomList,
 )
 
-
 GROUP_SERVER_SERVLET_CLASSES = (
     FederationGroupsProfileServlet,
     FederationGroupsSummaryServlet,
     FederationGroupsRoomsServlet,
     FederationGroupsUsersServlet,
+    FederationGroupsInvitedUsersServlet,
     FederationGroupsInviteServlet,
     FederationGroupsAcceptInviteServlet,
     FederationGroupsRemoveUserServlet,
diff --git a/synapse/groups/attestations.py b/synapse/groups/attestations.py
index 5ef7a12cb7..b751cf5e43 100644
--- a/synapse/groups/attestations.py
+++ b/synapse/groups/attestations.py
@@ -90,6 +90,7 @@ class GroupAttestionRenewer(object):
         self.assestations = hs.get_groups_attestation_signing()
         self.transport_client = hs.get_federation_transport_client()
         self.is_mine_id = hs.is_mine_id
+        self.attestations = hs.get_groups_attestation_signing()
 
         self._renew_attestations_loop = self.clock.looping_call(
             self._renew_attestations, 30 * 60 * 1000,
@@ -126,10 +127,10 @@ class GroupAttestionRenewer(object):
         )
 
         @defer.inlineCallbacks
-        def _renew_attestation(self, group_id, user_id):
+        def _renew_attestation(group_id, user_id):
             attestation = self.attestations.create_attestation(group_id, user_id)
 
-            if self.hs.is_mine_id(group_id):
+            if self.is_mine_id(group_id):
                 destination = get_domain_from_id(user_id)
             else:
                 destination = get_domain_from_id(group_id)
diff --git a/synapse/groups/groups_server.py b/synapse/groups/groups_server.py
index 1083bc2990..a3a500b9d6 100644
--- a/synapse/groups/groups_server.py
+++ b/synapse/groups/groups_server.py
@@ -420,6 +420,40 @@ class GroupsServerHandler(object):
             "total_user_count_estimate": len(user_results),
         })
 
+    @defer.inlineCallbacks
+    def get_invited_users_in_group(self, group_id, requester_user_id):
+        """Get the users that have been invited to a group as seen by requester_user_id.
+
+        The ordering is arbitrary at the moment
+        """
+
+        yield self.check_group_is_ours(group_id, and_exists=True)
+
+        is_user_in_group = yield self.store.is_user_in_group(requester_user_id, group_id)
+
+        if not is_user_in_group:
+            raise SynapseError(403, "User not in group")
+
+        invited_users = yield self.store.get_invited_users_in_group(group_id)
+
+        user_profiles = []
+
+        for user_id in invited_users:
+            user_profile = {
+                "user_id": user_id
+            }
+            try:
+                profile = yield self.profile_handler.get_profile_from_cache(user_id)
+                user_profile.update(profile)
+            except Exception as e:
+                logger.warn("Error getting profile for %s: %s", user_id, e)
+            user_profiles.append(user_profile)
+
+        defer.returnValue({
+            "chunk": user_profiles,
+            "total_user_count_estimate": len(invited_users),
+        })
+
     @defer.inlineCallbacks
     def get_rooms_in_group(self, group_id, requester_user_id):
         """Get the rooms in group as seen by requester_user_id
diff --git a/synapse/handlers/groups_local.py b/synapse/handlers/groups_local.py
index 3b676d46bd..6699d0888f 100644
--- a/synapse/handlers/groups_local.py
+++ b/synapse/handlers/groups_local.py
@@ -68,6 +68,8 @@ class GroupsLocalHandler(object):
     update_group_profile = _create_rerouter("update_group_profile")
     get_rooms_in_group = _create_rerouter("get_rooms_in_group")
 
+    get_invited_users_in_group = _create_rerouter("get_invited_users_in_group")
+
     add_room_to_group = _create_rerouter("add_room_to_group")
     remove_room_from_group = _create_rerouter("remove_room_from_group")
 
@@ -313,8 +315,11 @@ class GroupsLocalHandler(object):
         self.notifier.on_new_event(
             "groups_key", token, users=[user_id],
         )
-
-        user_profile = yield self.profile_handler.get_profile(user_id)
+        try:
+            user_profile = yield self.profile_handler.get_profile(user_id)
+        except Exception as e:
+            logger.warn("No profile for user %s: %s", user_id, e)
+            user_profile = {}
 
         defer.returnValue({"state": "invite", "user_profile": user_profile})
 
diff --git a/synapse/push/baserules.py b/synapse/push/baserules.py
index 9dce99ebec..7a18afe5f9 100644
--- a/synapse/push/baserules.py
+++ b/synapse/push/baserules.py
@@ -245,7 +245,7 @@ BASE_APPEND_OVERRIDE_RULES = [
             {
                 'kind': 'event_match',
                 'key': 'content.body',
-                'pattern': '*@room*',
+                'pattern': '@room',
                 '_id': '_roomnotif_content',
             },
             {
diff --git a/synapse/rest/client/v2_alpha/groups.py b/synapse/rest/client/v2_alpha/groups.py
index 8f3ce15b02..d11bccc1da 100644
--- a/synapse/rest/client/v2_alpha/groups.py
+++ b/synapse/rest/client/v2_alpha/groups.py
@@ -371,6 +371,27 @@ class GroupUsersServlet(RestServlet):
         defer.returnValue((200, result))
 
 
+class GroupInvitedUsersServlet(RestServlet):
+    """Get users invited to a group
+    """
+    PATTERNS = client_v2_patterns("/groups/(?P<group_id>[^/]*)/invited_users$")
+
+    def __init__(self, hs):
+        super(GroupInvitedUsersServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, group_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        result = yield self.groups_handler.get_invited_users_in_group(group_id, user_id)
+
+        defer.returnValue((200, result))
+
+
 class GroupCreateServlet(RestServlet):
     """Create a group
     """
@@ -674,6 +695,7 @@ class GroupsForUserServlet(RestServlet):
 def register_servlets(hs, http_server):
     GroupServlet(hs).register(http_server)
     GroupSummaryServlet(hs).register(http_server)
+    GroupInvitedUsersServlet(hs).register(http_server)
     GroupUsersServlet(hs).register(http_server)
     GroupRoomServlet(hs).register(http_server)
     GroupCreateServlet(hs).register(http_server)
diff --git a/synapse/rest/client/v2_alpha/register.py b/synapse/rest/client/v2_alpha/register.py
index 1421c18152..d9a8cdbbb5 100644
--- a/synapse/rest/client/v2_alpha/register.py
+++ b/synapse/rest/client/v2_alpha/register.py
@@ -17,8 +17,10 @@
 from twisted.internet import defer
 
 import synapse
+import synapse.types
 from synapse.api.auth import get_access_token_from_request, has_access_token
 from synapse.api.constants import LoginType
+from synapse.types import RoomID, RoomAlias
 from synapse.api.errors import SynapseError, Codes, UnrecognizedRequestError
 from synapse.http.servlet import (
     RestServlet, parse_json_object_from_request, assert_params_in_request, parse_string
@@ -170,6 +172,7 @@ class RegisterRestServlet(RestServlet):
         self.auth_handler = hs.get_auth_handler()
         self.registration_handler = hs.get_handlers().registration_handler
         self.identity_handler = hs.get_handlers().identity_handler
+        self.room_member_handler = hs.get_handlers().room_member_handler
         self.device_handler = hs.get_device_handler()
         self.macaroon_gen = hs.get_macaroon_generator()
 
@@ -340,6 +343,14 @@ class RegisterRestServlet(RestServlet):
                 generate_token=False,
             )
 
+            # auto-join the user to any rooms we're supposed to dump them into
+            fake_requester = synapse.types.create_requester(registered_user_id)
+            for r in self.hs.config.auto_join_rooms:
+                try:
+                    yield self._join_user_to_room(fake_requester, r)
+                except Exception as e:
+                    logger.error("Failed to join new user to %r: %r", r, e)
+
             # remember that we've now registered that user account, and with
             #  what user ID (since the user may not have specified)
             self.auth_handler.set_session_data(
@@ -372,6 +383,29 @@ class RegisterRestServlet(RestServlet):
     def on_OPTIONS(self, _):
         return 200, {}
 
+    @defer.inlineCallbacks
+    def _join_user_to_room(self, requester, room_identifier):
+        room_id = None
+        if RoomID.is_valid(room_identifier):
+            room_id = room_identifier
+        elif RoomAlias.is_valid(room_identifier):
+            room_alias = RoomAlias.from_string(room_identifier)
+            room_id, remote_room_hosts = (
+                yield self.room_member_handler.lookup_room_alias(room_alias)
+            )
+            room_id = room_id.to_string()
+        else:
+            raise SynapseError(400, "%s was not legal room ID or room alias" % (
+                room_identifier,
+            ))
+
+        yield self.room_member_handler.update_membership(
+            requester=requester,
+            target=requester.user,
+            room_id=room_id,
+            action="join",
+        )
+
     @defer.inlineCallbacks
     def _do_appservice_registration(self, username, as_token, body):
         user_id = yield self.registration_handler.appservice_register(
diff --git a/synapse/rest/media/v1/filepath.py b/synapse/rest/media/v1/filepath.py
index d5cec10127..d5164e47e0 100644
--- a/synapse/rest/media/v1/filepath.py
+++ b/synapse/rest/media/v1/filepath.py
@@ -15,80 +15,111 @@
 
 import os
 import re
+import functools
 
 NEW_FORMAT_ID_RE = re.compile(r"^\d\d\d\d-\d\d-\d\d")
 
 
+def _wrap_in_base_path(func):
+    """Takes a function that returns a relative path and turns it into an
+    absolute path based on the location of the primary media store
+    """
+    @functools.wraps(func)
+    def _wrapped(self, *args, **kwargs):
+        path = func(self, *args, **kwargs)
+        return os.path.join(self.base_path, path)
+
+    return _wrapped
+
+
 class MediaFilePaths(object):
+    """Describes where files are stored on disk.
 
-    def __init__(self, base_path):
-        self.base_path = base_path
+    Most of the functions have a `*_rel` variant which returns a file path that
+    is relative to the base media store path. This is mainly used when we want
+    to write to the backup media store (when one is configured)
+    """
 
-    def default_thumbnail(self, default_top_level, default_sub_type, width,
-                          height, content_type, method):
+    def __init__(self, primary_base_path):
+        self.base_path = primary_base_path
+
+    def default_thumbnail_rel(self, default_top_level, default_sub_type, width,
+                              height, content_type, method):
         top_level_type, sub_type = content_type.split("/")
         file_name = "%i-%i-%s-%s-%s" % (
             width, height, top_level_type, sub_type, method
         )
         return os.path.join(
-            self.base_path, "default_thumbnails", default_top_level,
+            "default_thumbnails", default_top_level,
             default_sub_type, file_name
         )
 
-    def local_media_filepath(self, media_id):
+    default_thumbnail = _wrap_in_base_path(default_thumbnail_rel)
+
+    def local_media_filepath_rel(self, media_id):
         return os.path.join(
-            self.base_path, "local_content",
+            "local_content",
             media_id[0:2], media_id[2:4], media_id[4:]
         )
 
-    def local_media_thumbnail(self, media_id, width, height, content_type,
-                              method):
+    local_media_filepath = _wrap_in_base_path(local_media_filepath_rel)
+
+    def local_media_thumbnail_rel(self, media_id, width, height, content_type,
+                                  method):
         top_level_type, sub_type = content_type.split("/")
         file_name = "%i-%i-%s-%s-%s" % (
             width, height, top_level_type, sub_type, method
         )
         return os.path.join(
-            self.base_path, "local_thumbnails",
+            "local_thumbnails",
             media_id[0:2], media_id[2:4], media_id[4:],
             file_name
         )
 
-    def remote_media_filepath(self, server_name, file_id):
+    local_media_thumbnail = _wrap_in_base_path(local_media_thumbnail_rel)
+
+    def remote_media_filepath_rel(self, server_name, file_id):
         return os.path.join(
-            self.base_path, "remote_content", server_name,
+            "remote_content", server_name,
             file_id[0:2], file_id[2:4], file_id[4:]
         )
 
-    def remote_media_thumbnail(self, server_name, file_id, width, height,
-                               content_type, method):
+    remote_media_filepath = _wrap_in_base_path(remote_media_filepath_rel)
+
+    def remote_media_thumbnail_rel(self, server_name, file_id, width, height,
+                                   content_type, method):
         top_level_type, sub_type = content_type.split("/")
         file_name = "%i-%i-%s-%s" % (width, height, top_level_type, sub_type)
         return os.path.join(
-            self.base_path, "remote_thumbnail", server_name,
+            "remote_thumbnail", server_name,
             file_id[0:2], file_id[2:4], file_id[4:],
             file_name
         )
 
+    remote_media_thumbnail = _wrap_in_base_path(remote_media_thumbnail_rel)
+
     def remote_media_thumbnail_dir(self, server_name, file_id):
         return os.path.join(
             self.base_path, "remote_thumbnail", server_name,
             file_id[0:2], file_id[2:4], file_id[4:],
         )
 
-    def url_cache_filepath(self, media_id):
+    def url_cache_filepath_rel(self, media_id):
         if NEW_FORMAT_ID_RE.match(media_id):
             # Media id is of the form <DATE><RANDOM_STRING>
             # E.g.: 2017-09-28-fsdRDt24DS234dsf
             return os.path.join(
-                self.base_path, "url_cache",
+                "url_cache",
                 media_id[:10], media_id[11:]
             )
         else:
             return os.path.join(
-                self.base_path, "url_cache",
+                "url_cache",
                 media_id[0:2], media_id[2:4], media_id[4:],
             )
 
+    url_cache_filepath = _wrap_in_base_path(url_cache_filepath_rel)
+
     def url_cache_filepath_dirs_to_delete(self, media_id):
         "The dirs to try and remove if we delete the media_id file"
         if NEW_FORMAT_ID_RE.match(media_id):
@@ -110,8 +141,8 @@ class MediaFilePaths(object):
                 ),
             ]
 
-    def url_cache_thumbnail(self, media_id, width, height, content_type,
-                            method):
+    def url_cache_thumbnail_rel(self, media_id, width, height, content_type,
+                                method):
         # Media id is of the form <DATE><RANDOM_STRING>
         # E.g.: 2017-09-28-fsdRDt24DS234dsf
 
@@ -122,17 +153,19 @@ class MediaFilePaths(object):
 
         if NEW_FORMAT_ID_RE.match(media_id):
             return os.path.join(
-                self.base_path, "url_cache_thumbnails",
+                "url_cache_thumbnails",
                 media_id[:10], media_id[11:],
                 file_name
             )
         else:
             return os.path.join(
-                self.base_path, "url_cache_thumbnails",
+                "url_cache_thumbnails",
                 media_id[0:2], media_id[2:4], media_id[4:],
                 file_name
             )
 
+    url_cache_thumbnail = _wrap_in_base_path(url_cache_thumbnail_rel)
+
     def url_cache_thumbnail_directory(self, media_id):
         # Media id is of the form <DATE><RANDOM_STRING>
         # E.g.: 2017-09-28-fsdRDt24DS234dsf
diff --git a/synapse/rest/media/v1/media_repository.py b/synapse/rest/media/v1/media_repository.py
index 0ea1248ce6..6b50b45b1f 100644
--- a/synapse/rest/media/v1/media_repository.py
+++ b/synapse/rest/media/v1/media_repository.py
@@ -33,7 +33,7 @@ from synapse.api.errors import SynapseError, HttpResponseException, \
 
 from synapse.util.async import Linearizer
 from synapse.util.stringutils import is_ascii
-from synapse.util.logcontext import preserve_context_over_fn
+from synapse.util.logcontext import make_deferred_yieldable, preserve_fn
 from synapse.util.retryutils import NotRetryingDestination
 
 import os
@@ -59,7 +59,14 @@ class MediaRepository(object):
         self.store = hs.get_datastore()
         self.max_upload_size = hs.config.max_upload_size
         self.max_image_pixels = hs.config.max_image_pixels
-        self.filepaths = MediaFilePaths(hs.config.media_store_path)
+
+        self.primary_base_path = hs.config.media_store_path
+        self.filepaths = MediaFilePaths(self.primary_base_path)
+
+        self.backup_base_path = hs.config.backup_media_store_path
+
+        self.synchronous_backup_media_store = hs.config.synchronous_backup_media_store
+
         self.dynamic_thumbnails = hs.config.dynamic_thumbnails
         self.thumbnail_requirements = hs.config.thumbnail_requirements
 
@@ -87,18 +94,86 @@ class MediaRepository(object):
         if not os.path.exists(dirname):
             os.makedirs(dirname)
 
+    @staticmethod
+    def _write_file_synchronously(source, fname):
+        """Write `source` to the path `fname` synchronously. Should be called
+        from a thread.
+
+        Args:
+            source: A file like object to be written
+            fname (str): Path to write to
+        """
+        MediaRepository._makedirs(fname)
+        source.seek(0)  # Ensure we read from the start of the file
+        with open(fname, "wb") as f:
+            shutil.copyfileobj(source, f)
+
+    @defer.inlineCallbacks
+    def write_to_file_and_backup(self, source, path):
+        """Write `source` to the on disk media store, and also the backup store
+        if configured.
+
+        Args:
+            source: A file like object that should be written
+            path (str): Relative path to write file to
+
+        Returns:
+            Deferred[str]: the file path written to in the primary media store
+        """
+        fname = os.path.join(self.primary_base_path, path)
+
+        # Write to the main repository
+        yield make_deferred_yieldable(threads.deferToThread(
+            self._write_file_synchronously, source, fname,
+        ))
+
+        # Write to backup repository
+        yield self.copy_to_backup(path)
+
+        defer.returnValue(fname)
+
+    @defer.inlineCallbacks
+    def copy_to_backup(self, path):
+        """Copy a file from the primary to backup media store, if configured.
+
+        Args:
+            path(str): Relative path to write file to
+        """
+        if self.backup_base_path:
+            primary_fname = os.path.join(self.primary_base_path, path)
+            backup_fname = os.path.join(self.backup_base_path, path)
+
+            # We can either wait for successful writing to the backup repository
+            # or write in the background and immediately return
+            if self.synchronous_backup_media_store:
+                yield make_deferred_yieldable(threads.deferToThread(
+                    shutil.copyfile, primary_fname, backup_fname,
+                ))
+            else:
+                preserve_fn(threads.deferToThread)(
+                    shutil.copyfile, primary_fname, backup_fname,
+                )
+
     @defer.inlineCallbacks
     def create_content(self, media_type, upload_name, content, content_length,
                        auth_user):
+        """Store uploaded content for a local user and return the mxc URL
+
+        Args:
+            media_type(str): The content type of the file
+            upload_name(str): The name of the file
+            content: A file like object that is the content to store
+            content_length(int): The length of the content
+            auth_user(str): The user_id of the uploader
+
+        Returns:
+            Deferred[str]: The mxc url of the stored content
+        """
         media_id = random_string(24)
 
-        fname = self.filepaths.local_media_filepath(media_id)
-        self._makedirs(fname)
-
-        # This shouldn't block for very long because the content will have
-        # already been uploaded at this point.
-        with open(fname, "wb") as f:
-            f.write(content)
+        fname = yield self.write_to_file_and_backup(
+            content, self.filepaths.local_media_filepath_rel(media_id)
+        )
 
         logger.info("Stored local media in file %r", fname)
 
@@ -115,7 +190,7 @@ class MediaRepository(object):
             "media_length": content_length,
         }
 
-        yield self._generate_local_thumbnails(media_id, media_info)
+        yield self._generate_thumbnails(None, media_id, media_info)
 
         defer.returnValue("mxc://%s/%s" % (self.server_name, media_id))
 
@@ -148,9 +223,10 @@ class MediaRepository(object):
     def _download_remote_file(self, server_name, media_id):
         file_id = random_string(24)
 
-        fname = self.filepaths.remote_media_filepath(
+        fpath = self.filepaths.remote_media_filepath_rel(
             server_name, file_id
         )
+        fname = os.path.join(self.primary_base_path, fpath)
         self._makedirs(fname)
 
         try:
@@ -192,6 +268,8 @@ class MediaRepository(object):
                                      server_name, media_id)
                     raise SynapseError(502, "Failed to fetch remote media")
 
+            yield self.copy_to_backup(fpath)
+
             media_type = headers["Content-Type"][0]
             time_now_ms = self.clock.time_msec()
 
@@ -244,7 +322,7 @@ class MediaRepository(object):
             "filesystem_id": file_id,
         }
 
-        yield self._generate_remote_thumbnails(
+        yield self._generate_thumbnails(
             server_name, media_id, media_info
         )
 
@@ -253,9 +331,8 @@ class MediaRepository(object):
     def _get_thumbnail_requirements(self, media_type):
         return self.thumbnail_requirements.get(media_type, ())
 
-    def _generate_thumbnail(self, input_path, t_path, t_width, t_height,
+    def _generate_thumbnail(self, thumbnailer, t_width, t_height,
                             t_method, t_type):
-        thumbnailer = Thumbnailer(input_path)
         m_width = thumbnailer.width
         m_height = thumbnailer.height
 
@@ -267,72 +344,105 @@ class MediaRepository(object):
             return
 
         if t_method == "crop":
-            t_len = thumbnailer.crop(t_path, t_width, t_height, t_type)
+            t_byte_source = thumbnailer.crop(t_width, t_height, t_type)
         elif t_method == "scale":
             t_width, t_height = thumbnailer.aspect(t_width, t_height)
             t_width = min(m_width, t_width)
             t_height = min(m_height, t_height)
-            t_len = thumbnailer.scale(t_path, t_width, t_height, t_type)
+            t_byte_source = thumbnailer.scale(t_width, t_height, t_type)
         else:
-            t_len = None
+            t_byte_source = None
 
-        return t_len
+        return t_byte_source
 
     @defer.inlineCallbacks
     def generate_local_exact_thumbnail(self, media_id, t_width, t_height,
                                        t_method, t_type):
         input_path = self.filepaths.local_media_filepath(media_id)
 
-        t_path = self.filepaths.local_media_thumbnail(
-            media_id, t_width, t_height, t_type, t_method
-        )
-        self._makedirs(t_path)
-
-        t_len = yield preserve_context_over_fn(
-            threads.deferToThread,
+        thumbnailer = Thumbnailer(input_path)
+        t_byte_source = yield make_deferred_yieldable(threads.deferToThread(
             self._generate_thumbnail,
-            input_path, t_path, t_width, t_height, t_method, t_type
-        )
+            thumbnailer, t_width, t_height, t_method, t_type
+        ))
+
+        if t_byte_source:
+            try:
+                output_path = yield self.write_to_file_and_backup(
+                    t_byte_source,
+                    self.filepaths.local_media_thumbnail_rel(
+                        media_id, t_width, t_height, t_type, t_method
+                    )
+                )
+            finally:
+                t_byte_source.close()
+
+            logger.info("Stored thumbnail in file %r", output_path)
+
+            t_len = os.path.getsize(output_path)
 
-        if t_len:
             yield self.store.store_local_thumbnail(
                 media_id, t_width, t_height, t_type, t_method, t_len
             )
 
-            defer.returnValue(t_path)
+            defer.returnValue(output_path)
 
     @defer.inlineCallbacks
     def generate_remote_exact_thumbnail(self, server_name, file_id, media_id,
                                         t_width, t_height, t_method, t_type):
         input_path = self.filepaths.remote_media_filepath(server_name, file_id)
 
-        t_path = self.filepaths.remote_media_thumbnail(
-            server_name, file_id, t_width, t_height, t_type, t_method
-        )
-        self._makedirs(t_path)
-
-        t_len = yield preserve_context_over_fn(
-            threads.deferToThread,
+        thumbnailer = Thumbnailer(input_path)
+        t_byte_source = yield make_deferred_yieldable(threads.deferToThread(
             self._generate_thumbnail,
-            input_path, t_path, t_width, t_height, t_method, t_type
-        )
+            thumbnailer, t_width, t_height, t_method, t_type
+        ))
+
+        if t_byte_source:
+            try:
+                output_path = yield self.write_to_file_and_backup(
+                    t_byte_source,
+                    self.filepaths.remote_media_thumbnail_rel(
+                        server_name, file_id, t_width, t_height, t_type, t_method
+                    )
+                )
+            finally:
+                t_byte_source.close()
+
+            logger.info("Stored thumbnail in file %r", output_path)
+
+            t_len = os.path.getsize(output_path)
 
-        if t_len:
             yield self.store.store_remote_media_thumbnail(
                 server_name, media_id, file_id,
                 t_width, t_height, t_type, t_method, t_len
             )
 
-            defer.returnValue(t_path)
+            defer.returnValue(output_path)
 
     @defer.inlineCallbacks
-    def _generate_local_thumbnails(self, media_id, media_info, url_cache=False):
+    def _generate_thumbnails(self, server_name, media_id, media_info, url_cache=False):
+        """Generate and store thumbnails for an image.
+
+        Args:
+            server_name(str|None): The server name if remote media, else None if local
+            media_id(str)
+            media_info(dict)
+            url_cache(bool): If we are thumbnailing images downloaded for the URL cache,
+                used exclusively by the url previewer
+
+        Returns:
+            Deferred[dict]: Dict with "width" and "height" keys of original image
+        """
         media_type = media_info["media_type"]
+        file_id = media_info.get("filesystem_id")
         requirements = self._get_thumbnail_requirements(media_type)
         if not requirements:
             return
 
-        if url_cache:
+        if server_name:
+            input_path = self.filepaths.remote_media_filepath(server_name, file_id)
+        elif url_cache:
             input_path = self.filepaths.url_cache_filepath(media_id)
         else:
             input_path = self.filepaths.local_media_filepath(media_id)
@@ -348,135 +458,72 @@ class MediaRepository(object):
             )
             return
 
-        local_thumbnails = []
+        # We deduplicate the thumbnail sizes by ignoring the cropped versions if
+        # they have the same dimensions of a scaled one.
+        thumbnails = {}
+        for r_width, r_height, r_method, r_type in requirements:
+            if r_method == "crop":
+                thumbnails.setdefault((r_width, r_height, r_type), r_method)
+            elif r_method == "scale":
+                t_width, t_height = thumbnailer.aspect(r_width, r_height)
+                t_width = min(m_width, t_width)
+                t_height = min(m_height, t_height)
+                thumbnails[(t_width, t_height, r_type)] = r_method
 
-        def generate_thumbnails():
-            scales = set()
-            crops = set()
-            for r_width, r_height, r_method, r_type in requirements:
-                if r_method == "scale":
-                    t_width, t_height = thumbnailer.aspect(r_width, r_height)
-                    scales.add((
-                        min(m_width, t_width), min(m_height, t_height), r_type,
-                    ))
-                elif r_method == "crop":
-                    crops.add((r_width, r_height, r_type))
-
-            for t_width, t_height, t_type in scales:
-                t_method = "scale"
-                if url_cache:
-                    t_path = self.filepaths.url_cache_thumbnail(
-                        media_id, t_width, t_height, t_type, t_method
-                    )
-                else:
-                    t_path = self.filepaths.local_media_thumbnail(
-                        media_id, t_width, t_height, t_type, t_method
-                    )
-                self._makedirs(t_path)
-                t_len = thumbnailer.scale(t_path, t_width, t_height, t_type)
-
-                local_thumbnails.append((
-                    media_id, t_width, t_height, t_type, t_method, t_len
-                ))
-
-            for t_width, t_height, t_type in crops:
-                if (t_width, t_height, t_type) in scales:
-                    # If the aspect ratio of the cropped thumbnail matches a purely
-                    # scaled one then there is no point in calculating a separate
-                    # thumbnail.
-                    continue
-                t_method = "crop"
-                if url_cache:
-                    t_path = self.filepaths.url_cache_thumbnail(
-                        media_id, t_width, t_height, t_type, t_method
-                    )
-                else:
-                    t_path = self.filepaths.local_media_thumbnail(
-                        media_id, t_width, t_height, t_type, t_method
-                    )
-                self._makedirs(t_path)
-                t_len = thumbnailer.crop(t_path, t_width, t_height, t_type)
-                local_thumbnails.append((
-                    media_id, t_width, t_height, t_type, t_method, t_len
-                ))
-
-        yield preserve_context_over_fn(threads.deferToThread, generate_thumbnails)
-
-        for l in local_thumbnails:
-            yield self.store.store_local_thumbnail(*l)
-
-        defer.returnValue({
-            "width": m_width,
-            "height": m_height,
-        })
-
-    @defer.inlineCallbacks
-    def _generate_remote_thumbnails(self, server_name, media_id, media_info):
-        media_type = media_info["media_type"]
-        file_id = media_info["filesystem_id"]
-        requirements = self._get_thumbnail_requirements(media_type)
-        if not requirements:
-            return
-
-        remote_thumbnails = []
-
-        input_path = self.filepaths.remote_media_filepath(server_name, file_id)
-        thumbnailer = Thumbnailer(input_path)
-        m_width = thumbnailer.width
-        m_height = thumbnailer.height
-
-        def generate_thumbnails():
-            if m_width * m_height >= self.max_image_pixels:
-                logger.info(
-                    "Image too large to thumbnail %r x %r > %r",
-                    m_width, m_height, self.max_image_pixels
-                )
-                return
-
-            scales = set()
-            crops = set()
-            for r_width, r_height, r_method, r_type in requirements:
-                if r_method == "scale":
-                    t_width, t_height = thumbnailer.aspect(r_width, r_height)
-                    scales.add((
-                        min(m_width, t_width), min(m_height, t_height), r_type,
-                    ))
-                elif r_method == "crop":
-                    crops.add((r_width, r_height, r_type))
-
-            for t_width, t_height, t_type in scales:
-                t_method = "scale"
-                t_path = self.filepaths.remote_media_thumbnail(
+        # Now we generate the thumbnails for each dimension, store it
+        for (t_width, t_height, t_type), t_method in thumbnails.iteritems():
+            # Work out the correct file name for thumbnail
+            if server_name:
+                file_path = self.filepaths.remote_media_thumbnail_rel(
                     server_name, file_id, t_width, t_height, t_type, t_method
                 )
-                self._makedirs(t_path)
-                t_len = thumbnailer.scale(t_path, t_width, t_height, t_type)
-                remote_thumbnails.append([
-                    server_name, media_id, file_id,
-                    t_width, t_height, t_type, t_method, t_len
-                ])
-
-            for t_width, t_height, t_type in crops:
-                if (t_width, t_height, t_type) in scales:
-                    # If the aspect ratio of the cropped thumbnail matches a purely
-                    # scaled one then there is no point in calculating a separate
-                    # thumbnail.
-                    continue
-                t_method = "crop"
-                t_path = self.filepaths.remote_media_thumbnail(
-                    server_name, file_id, t_width, t_height, t_type, t_method
+            elif url_cache:
+                file_path = self.filepaths.url_cache_thumbnail_rel(
+                    media_id, t_width, t_height, t_type, t_method
                 )
-                self._makedirs(t_path)
-                t_len = thumbnailer.crop(t_path, t_width, t_height, t_type)
-                remote_thumbnails.append([
+            else:
+                file_path = self.filepaths.local_media_thumbnail_rel(
+                    media_id, t_width, t_height, t_type, t_method
+                )
+
+            # Generate the thumbnail
+            if t_method == "crop":
+                t_byte_source = yield make_deferred_yieldable(threads.deferToThread(
+                    thumbnailer.crop,
+                    t_width, t_height, t_type,
+                ))
+            elif t_method == "scale":
+                t_byte_source = yield make_deferred_yieldable(threads.deferToThread(
+                    thumbnailer.scale,
+                    t_width, t_height, t_type,
+                ))
+            else:
+                logger.error("Unrecognized method: %r", t_method)
+                continue
+
+            if not t_byte_source:
+                continue
+
+            try:
+                # Write to disk
+                output_path = yield self.write_to_file_and_backup(
+                    t_byte_source, file_path,
+                )
+            finally:
+                t_byte_source.close()
+
+            t_len = os.path.getsize(output_path)
+
+            # Write to database
+            if server_name:
+                yield self.store.store_remote_media_thumbnail(
                     server_name, media_id, file_id,
                     t_width, t_height, t_type, t_method, t_len
-                ])
-
-        yield preserve_context_over_fn(threads.deferToThread, generate_thumbnails)
-
-        for r in remote_thumbnails:
-            yield self.store.store_remote_media_thumbnail(*r)
+                )
+            else:
+                yield self.store.store_local_thumbnail(
+                    media_id, t_width, t_height, t_type, t_method, t_len
+                )
 
         defer.returnValue({
             "width": m_width,
@@ -497,6 +544,8 @@ class MediaRepository(object):
 
             logger.info("Deleting: %r", key)
 
+            # TODO: Should we delete from the backup store
+
             with (yield self.remote_media_linearizer.queue(key)):
                 full_path = self.filepaths.remote_media_filepath(origin, file_id)
                 try:
diff --git a/synapse/rest/media/v1/preview_url_resource.py b/synapse/rest/media/v1/preview_url_resource.py
index 895b480d5c..2a3e37fdf4 100644
--- a/synapse/rest/media/v1/preview_url_resource.py
+++ b/synapse/rest/media/v1/preview_url_resource.py
@@ -59,6 +59,7 @@ class PreviewUrlResource(Resource):
         self.store = hs.get_datastore()
         self.client = SpiderHttpClient(hs)
         self.media_repo = media_repo
+        self.primary_base_path = media_repo.primary_base_path
 
         self.url_preview_url_blacklist = hs.config.url_preview_url_blacklist
 
@@ -170,8 +171,8 @@ class PreviewUrlResource(Resource):
         logger.debug("got media_info of '%s'" % media_info)
 
         if _is_media(media_info['media_type']):
-            dims = yield self.media_repo._generate_local_thumbnails(
-                media_info['filesystem_id'], media_info, url_cache=True,
+            dims = yield self.media_repo._generate_thumbnails(
+                None, media_info['filesystem_id'], media_info, url_cache=True,
             )
 
             og = {
@@ -216,8 +217,8 @@ class PreviewUrlResource(Resource):
 
                 if _is_media(image_info['media_type']):
                     # TODO: make sure we don't choke on white-on-transparent images
-                    dims = yield self.media_repo._generate_local_thumbnails(
-                        image_info['filesystem_id'], image_info, url_cache=True,
+                    dims = yield self.media_repo._generate_thumbnails(
+                        None, image_info['filesystem_id'], image_info, url_cache=True,
                     )
                     if dims:
                         og["og:image:width"] = dims['width']
@@ -262,7 +263,8 @@ class PreviewUrlResource(Resource):
 
         file_id = datetime.date.today().isoformat() + '_' + random_string(16)
 
-        fname = self.filepaths.url_cache_filepath(file_id)
+        fpath = self.filepaths.url_cache_filepath_rel(file_id)
+        fname = os.path.join(self.primary_base_path, fpath)
         self.media_repo._makedirs(fname)
 
         try:
@@ -273,6 +275,8 @@ class PreviewUrlResource(Resource):
                 )
                 # FIXME: pass through 404s and other error messages nicely
 
+            yield self.media_repo.copy_to_backup(fpath)
+
             media_type = headers["Content-Type"][0]
             time_now_ms = self.clock.time_msec()
 
@@ -338,6 +342,9 @@ class PreviewUrlResource(Resource):
     def _expire_url_cache_data(self):
         """Clean up expired url cache content, media and thumbnails.
         """
+
+        # TODO: Delete from backup media store
+
         now = self.clock.time_msec()
 
         # First we delete expired url cache entries
diff --git a/synapse/rest/media/v1/thumbnailer.py b/synapse/rest/media/v1/thumbnailer.py
index 3868d4f65f..e1ee535b9a 100644
--- a/synapse/rest/media/v1/thumbnailer.py
+++ b/synapse/rest/media/v1/thumbnailer.py
@@ -50,12 +50,16 @@ class Thumbnailer(object):
         else:
             return ((max_height * self.width) // self.height, max_height)
 
-    def scale(self, output_path, width, height, output_type):
-        """Rescales the image to the given dimensions"""
-        scaled = self.image.resize((width, height), Image.ANTIALIAS)
-        return self.save_image(scaled, output_type, output_path)
+    def scale(self, width, height, output_type):
+        """Rescales the image to the given dimensions.
 
-    def crop(self, output_path, width, height, output_type):
+        Returns:
+            BytesIO: the bytes of the encoded image ready to be written to disk
+        """
+        scaled = self.image.resize((width, height), Image.ANTIALIAS)
+        return self._encode_image(scaled, output_type)
+
+    def crop(self, width, height, output_type):
         """Rescales and crops the image to the given dimensions preserving
         aspect::
             (w_in / h_in) = (w_scaled / h_scaled)
@@ -65,6 +69,9 @@ class Thumbnailer(object):
         Args:
             max_width: The largest possible width.
             max_height: The larget possible height.
+
+        Returns:
+            BytesIO: the bytes of the encoded image ready to be written to disk
         """
         if width * self.height > height * self.width:
             scaled_height = (width * self.height) // self.width
@@ -82,13 +89,9 @@ class Thumbnailer(object):
             crop_left = (scaled_width - width) // 2
             crop_right = width + crop_left
             cropped = scaled_image.crop((crop_left, 0, crop_right, height))
-        return self.save_image(cropped, output_type, output_path)
+        return self._encode_image(cropped, output_type)
 
-    def save_image(self, output_image, output_type, output_path):
+    def _encode_image(self, output_image, output_type):
         output_bytes_io = BytesIO()
         output_image.save(output_bytes_io, self.FORMATS[output_type], quality=80)
-        output_bytes = output_bytes_io.getvalue()
-        with open(output_path, "wb") as output_file:
-            output_file.write(output_bytes)
-        logger.info("Stored thumbnail in file %r", output_path)
-        return len(output_bytes)
+        return output_bytes_io
diff --git a/synapse/rest/media/v1/upload_resource.py b/synapse/rest/media/v1/upload_resource.py
index 4ab33f73bf..f6f498cdc5 100644
--- a/synapse/rest/media/v1/upload_resource.py
+++ b/synapse/rest/media/v1/upload_resource.py
@@ -93,7 +93,7 @@ class UploadResource(Resource):
         # TODO(markjh): parse content-dispostion
 
         content_uri = yield self.media_repo.create_content(
-            media_type, upload_name, request.content.read(),
+            media_type, upload_name, request.content,
             content_length, requester.user
         )
 
diff --git a/synapse/server.pyi b/synapse/server.pyi
index 9570df5537..e8c0386b7f 100644
--- a/synapse/server.pyi
+++ b/synapse/server.pyi
@@ -1,4 +1,6 @@
 import synapse.api.auth
+import synapse.federation.transaction_queue
+import synapse.federation.transport.client
 import synapse.handlers
 import synapse.handlers.auth
 import synapse.handlers.device
@@ -27,3 +29,9 @@ class HomeServer(object):
 
     def get_state_handler(self) -> synapse.state.StateHandler:
         pass
+
+    def get_federation_sender(self) -> synapse.federation.transaction_queue.TransactionQueue:
+        pass
+
+    def get_federation_transport_client(self) -> synapse.federation.transport.client.TransportLayerClient:
+        pass
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 752f172058..ad5c6f7c65 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -21,7 +21,7 @@ from synapse.events.utils import prune_event
 
 from synapse.util.async import ObservableDeferred
 from synapse.util.logcontext import (
-    preserve_fn, PreserveLoggingContext, preserve_context_over_deferred
+    preserve_fn, PreserveLoggingContext, make_deferred_yieldable
 )
 from synapse.util.logutils import log_function
 from synapse.util.metrics import Measure
@@ -88,13 +88,23 @@ class _EventPeristenceQueue(object):
     def add_to_queue(self, room_id, events_and_contexts, backfilled):
         """Add events to the queue, with the given persist_event options.
 
+        NB: due to the normal usage pattern of this method, it does *not*
+        follow the synapse logcontext rules, and leaves the logcontext in
+        place whether or not the returned deferred is ready.
+
         Args:
             room_id (str):
             events_and_contexts (list[(EventBase, EventContext)]):
             backfilled (bool):
+
+        Returns:
+            defer.Deferred: a deferred which will resolve once the events are
+                persisted. Runs its callbacks *without* a logcontext.
         """
         queue = self._event_persist_queues.setdefault(room_id, deque())
         if queue:
+            # if the last item in the queue has the same `backfilled` setting,
+            # we can just add these new events to that item.
             end_item = queue[-1]
             if end_item.backfilled == backfilled:
                 end_item.events_and_contexts.extend(events_and_contexts)
@@ -113,11 +123,11 @@ class _EventPeristenceQueue(object):
     def handle_queue(self, room_id, per_item_callback):
         """Attempts to handle the queue for a room if not already being handled.
 
-        The given callback will be invoked with for each item in the queue,1
+        The given callback will be invoked with for each item in the queue,
         of type _EventPersistQueueItem. The per_item_callback will continuously
         be called with new items, unless the queue becomnes empty. The return
         value of the function will be given to the deferreds waiting on the item,
-        exceptions will be passed to the deferres as well.
+        exceptions will be passed to the deferreds as well.
 
         This function should therefore be called whenever anything is added
         to the queue.
@@ -233,7 +243,7 @@ class EventsStore(SQLBaseStore):
 
         deferreds = []
         for room_id, evs_ctxs in partitioned.iteritems():
-            d = preserve_fn(self._event_persist_queue.add_to_queue)(
+            d = self._event_persist_queue.add_to_queue(
                 room_id, evs_ctxs,
                 backfilled=backfilled,
             )
@@ -242,7 +252,7 @@ class EventsStore(SQLBaseStore):
         for room_id in partitioned:
             self._maybe_start_persisting(room_id)
 
-        return preserve_context_over_deferred(
+        return make_deferred_yieldable(
             defer.gatherResults(deferreds, consumeErrors=True)
         )
 
@@ -267,7 +277,7 @@ class EventsStore(SQLBaseStore):
 
         self._maybe_start_persisting(event.room_id)
 
-        yield preserve_context_over_deferred(deferred)
+        yield make_deferred_yieldable(deferred)
 
         max_persisted_id = yield self._stream_id_gen.get_current_token()
         defer.returnValue((event.internal_metadata.stream_ordering, max_persisted_id))
@@ -1525,7 +1535,7 @@ class EventsStore(SQLBaseStore):
         if not allow_rejected:
             rows[:] = [r for r in rows if not r["rejects"]]
 
-        res = yield preserve_context_over_deferred(defer.gatherResults(
+        res = yield make_deferred_yieldable(defer.gatherResults(
             [
                 preserve_fn(self._get_event_from_row)(
                     row["internal_metadata"], row["json"], row["redacts"],
diff --git a/synapse/storage/group_server.py b/synapse/storage/group_server.py
index 3af372de59..9e63db5c6c 100644
--- a/synapse/storage/group_server.py
+++ b/synapse/storage/group_server.py
@@ -56,6 +56,18 @@ class GroupServerStore(SQLBaseStore):
             desc="get_users_in_group",
         )
 
+    def get_invited_users_in_group(self, group_id):
+        # TODO: Pagination
+
+        return self._simple_select_onecol(
+            table="group_invites",
+            keyvalues={
+                "group_id": group_id,
+            },
+            retcol="user_id",
+            desc="get_invited_users_in_group",
+        )
+
     def get_rooms_in_group(self, group_id, include_private=False):
         # TODO: Pagination
 
diff --git a/synapse/util/async.py b/synapse/util/async.py
index 0fd5b42523..a0a9039475 100644
--- a/synapse/util/async.py
+++ b/synapse/util/async.py
@@ -53,6 +53,11 @@ class ObservableDeferred(object):
 
     Cancelling or otherwise resolving an observer will not affect the original
     ObservableDeferred.
+
+    NB that it does not attempt to do anything with logcontexts; in general
+    you should probably make_deferred_yieldable the deferreds
+    returned by `observe`, and ensure that the original deferred runs its
+    callbacks in the sentinel logcontext.
     """
 
     __slots__ = ["_deferred", "_observers", "_result"]
diff --git a/tests/rest/client/v2_alpha/test_register.py b/tests/rest/client/v2_alpha/test_register.py
index b6173ab2ee..821c735528 100644
--- a/tests/rest/client/v2_alpha/test_register.py
+++ b/tests/rest/client/v2_alpha/test_register.py
@@ -47,6 +47,7 @@ class RegisterRestServletTestCase(unittest.TestCase):
         self.hs.get_auth_handler = Mock(return_value=self.auth_handler)
         self.hs.get_device_handler = Mock(return_value=self.device_handler)
         self.hs.config.enable_registration = True
+        self.hs.config.auto_join_rooms = []
 
         # init the thing we're testing
         self.servlet = RegisterRestServlet(self.hs)
diff --git a/tests/storage/event_injector.py b/tests/storage/event_injector.py
deleted file mode 100644
index 024ac15069..0000000000
--- a/tests/storage/event_injector.py
+++ /dev/null
@@ -1,76 +0,0 @@
-# -*- coding: utf-8 -*-
-# Copyright 2015, 2016 OpenMarket Ltd
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-
-from twisted.internet import defer
-
-from synapse.api.constants import EventTypes
-
-
-class EventInjector:
-    def __init__(self, hs):
-        self.hs = hs
-        self.store = hs.get_datastore()
-        self.message_handler = hs.get_handlers().message_handler
-        self.event_builder_factory = hs.get_event_builder_factory()
-
-    @defer.inlineCallbacks
-    def create_room(self, room, user):
-        builder = self.event_builder_factory.new({
-            "type": EventTypes.Create,
-            "sender": user.to_string(),
-            "room_id": room.to_string(),
-            "content": {},
-        })
-
-        event, context = yield self.message_handler._create_new_client_event(
-            builder
-        )
-
-        yield self.store.persist_event(event, context)
-
-    @defer.inlineCallbacks
-    def inject_room_member(self, room, user, membership):
-        builder = self.event_builder_factory.new({
-            "type": EventTypes.Member,
-            "sender": user.to_string(),
-            "state_key": user.to_string(),
-            "room_id": room.to_string(),
-            "content": {"membership": membership},
-        })
-
-        event, context = yield self.message_handler._create_new_client_event(
-            builder
-        )
-
-        yield self.store.persist_event(event, context)
-
-        defer.returnValue(event)
-
-    @defer.inlineCallbacks
-    def inject_message(self, room, user, body):
-        builder = self.event_builder_factory.new({
-            "type": EventTypes.Message,
-            "sender": user.to_string(),
-            "state_key": user.to_string(),
-            "room_id": room.to_string(),
-            "content": {"body": body, "msgtype": u"message"},
-        })
-
-        event, context = yield self.message_handler._create_new_client_event(
-            builder
-        )
-
-        yield self.store.persist_event(event, context)
diff --git a/tests/util/test_log_context.py b/tests/util/test_logcontext.py
similarity index 69%
rename from tests/util/test_log_context.py
rename to tests/util/test_logcontext.py
index 9ffe209c4d..e2f7765f49 100644
--- a/tests/util/test_log_context.py
+++ b/tests/util/test_logcontext.py
@@ -94,3 +94,41 @@ class LoggingContextTestCase(unittest.TestCase):
                 yield defer.succeed(None)
 
         return self._test_preserve_fn(nonblocking_function)
+
+    @defer.inlineCallbacks
+    def test_make_deferred_yieldable(self):
+        # a function which retuns an incomplete deferred, but doesn't follow
+        # the synapse rules.
+        def blocking_function():
+            d = defer.Deferred()
+            reactor.callLater(0, d.callback, None)
+            return d
+
+        sentinel_context = LoggingContext.current_context()
+
+        with LoggingContext() as context_one:
+            context_one.test_key = "one"
+
+            d1 = logcontext.make_deferred_yieldable(blocking_function())
+            # make sure that the context was reset by make_deferred_yieldable
+            self.assertIs(LoggingContext.current_context(), sentinel_context)
+
+            yield d1
+
+            # now it should be restored
+            self._check_test_key("one")
+
+    @defer.inlineCallbacks
+    def test_make_deferred_yieldable_on_non_deferred(self):
+        """Check that make_deferred_yieldable does the right thing when its
+        argument isn't actually a deferred"""
+
+        with LoggingContext() as context_one:
+            context_one.test_key = "one"
+
+            d1 = logcontext.make_deferred_yieldable("bum")
+            self._check_test_key("one")
+
+            r = yield d1
+            self.assertEqual(r, "bum")
+            self._check_test_key("one")