mirror of https://github.com/ceph/ceph
410 lines
15 KiB
ReStructuredText
410 lines
15 KiB
ReStructuredText
================
|
|
CephFS Mirroring
|
|
================
|
|
|
|
CephFS supports asynchronous replication of snapshots to a remote CephFS file
|
|
system via `cephfs-mirror` tool. Snapshots are synchronized by mirroring
|
|
snapshot data followed by creating a snapshot with the same name (for a given
|
|
directory on the remote file system) as the snapshot being synchronized.
|
|
|
|
Requirements
|
|
------------
|
|
|
|
The primary (local) and secondary (remote) Ceph clusters version should be
|
|
Pacific or later.
|
|
|
|
Key Idea
|
|
--------
|
|
|
|
For a given snapshot pair in a directory, `cephfs-mirror` daemon will rely on
|
|
readdir diff to identify changes in a directory tree. The diffs are applied to
|
|
directory in the remote file system thereby only synchronizing files that have
|
|
changed between two snapshots.
|
|
|
|
This feature is tracked here: https://tracker.ceph.com/issues/47034.
|
|
|
|
Currently, snapshot data is synchronized by bulk copying to the remote
|
|
filesystem.
|
|
|
|
.. note:: Synchronizing hardlinks is not supported -- hardlinked files get
|
|
synchronized as separate files.
|
|
|
|
Creating Users
|
|
--------------
|
|
|
|
Start by creating a user (on the primary/local cluster) for the mirror daemon.
|
|
This user requires write capability on the metadata pool to create RADOS
|
|
objects (index objects) for watch/notify operation and read capability on the
|
|
data pool(s).
|
|
|
|
.. prompt:: bash $
|
|
|
|
ceph auth get-or-create client.mirror mon 'profile cephfs-mirror' mds 'allow r' osd 'allow rw tag cephfs metadata=*, allow r tag cephfs data=*' mgr 'allow r'
|
|
|
|
Create a user for each file system peer (on the secondary/remote cluster). This user needs
|
|
to have full capabilities on the MDS (to take snapshots) and the OSDs::
|
|
|
|
$ ceph fs authorize <fs_name> client.mirror_remote / rwps
|
|
|
|
This user should be used (as part of peer specification) when adding a peer.
|
|
|
|
Starting Mirror Daemon
|
|
----------------------
|
|
|
|
Mirror daemon should be spawned using `systemctl(1)` unit files::
|
|
|
|
$ systemctl enable cephfs-mirror@mirror
|
|
$ systemctl start cephfs-mirror@mirror
|
|
|
|
`cephfs-mirror` daemon can be run in foreground using::
|
|
|
|
$ cephfs-mirror --id mirror --cluster site-a -f
|
|
|
|
.. note:: User used here is `mirror` as created in the `Creating Users` section.
|
|
|
|
Mirroring Design
|
|
----------------
|
|
|
|
CephFS supports asynchronous replication of snapshots to a remote CephFS file system
|
|
via `cephfs-mirror` tool. For a given directory, snapshots are synchronized by transferring
|
|
snapshot data to the remote file system and creating a snapshot with the same name as the
|
|
snapshot being synchronized.
|
|
|
|
Snapshot Synchronization Order
|
|
------------------------------
|
|
|
|
Although the order in which snapshots get chosen for synchronization does not matter,
|
|
snapshots are picked based on creation order (using snap-id).
|
|
|
|
Snapshot Incarnation
|
|
--------------------
|
|
|
|
A snapshot may be deleted and recreated (with the same name) with different contents.
|
|
An "old" snapshot could have been synchronized (earlier) and the recreation of the
|
|
snapshot could have been done when mirroring was disabled. Using snapshot names to
|
|
infer the point-of-continuation would result in the "new" snapshot (incarnation)
|
|
never getting picked up for synchronization.
|
|
|
|
Snapshots on the secondary file system stores the snap-id of the snapshot it was
|
|
synchronized from. This metadata is stored in `SnapInfo` structure on the MDS.
|
|
|
|
Interfaces
|
|
----------
|
|
|
|
`Mirroring` module (manager plugin) provides interfaces for managing directory snapshot
|
|
mirroring. Manager interfaces are (mostly) wrappers around monitor commands for managing
|
|
file system mirroring and is the recommended control interface.
|
|
|
|
Mirroring Module and Interface
|
|
------------------------------
|
|
|
|
Mirroring module provides interface for managing directory snapshot mirroring. The module
|
|
is implemented as a Ceph Manager plugin. Mirroring module does not manage spawning (and
|
|
terminating) the mirror daemons. Right now the preferred way would be to start/stop
|
|
mirror daemons via `systemctl(1)`. Going forward, deploying mirror daemons would be
|
|
managed by `cephadm` (Tracker: http://tracker.ceph.com/issues/47261).
|
|
|
|
The manager module is responsible for assigning directories to mirror daemons for
|
|
synchronization. Multiple mirror daemons can be spawned to achieve concurrency in
|
|
directory snapshot synchronization. When mirror daemons are spawned (or terminated)
|
|
, the mirroring module discovers the modified set of mirror daemons and rebalances
|
|
the directory assignment amongst the new set thus providing high-availability.
|
|
|
|
.. note:: Multiple mirror daemons is currently untested. Only a single mirror daemon
|
|
is recommended.
|
|
|
|
Mirroring module is disabled by default. To enable mirroring use::
|
|
|
|
$ ceph mgr module enable mirroring
|
|
|
|
Mirroring module provides a family of commands to control mirroring of directory
|
|
snapshots. To add or remove directories, mirroring needs to be enabled for a given
|
|
file system. To enable mirroring use::
|
|
|
|
$ ceph fs snapshot mirror enable <fs_name>
|
|
|
|
.. note:: Mirroring module commands use `fs snapshot mirror` prefix as compared to
|
|
the monitor commands which `fs mirror` prefix. Make sure to use module
|
|
commands.
|
|
|
|
To disable mirroring, use::
|
|
|
|
$ ceph fs snapshot mirror disable <fs_name>
|
|
|
|
Once mirroring is enabled, add a peer to which directory snapshots are to be mirrored.
|
|
Peers follow `<client>@<cluster>` specification and get assigned a unique-id (UUID)
|
|
when added. See `Creating Users` section on how to create Ceph users for mirroring.
|
|
|
|
To add a peer use::
|
|
|
|
$ ceph fs snapshot mirror peer_add <fs_name> <remote_cluster_spec> [<remote_fs_name>] [<remote_mon_host>] [<cephx_key>]
|
|
|
|
`<remote_fs_name>` is optional, and default to `<fs_name>` (on the remote cluster).
|
|
|
|
This requires the remote cluster ceph configuration and user keyring to be available in
|
|
the primary cluster. See `Bootstrap Peers` section to avoid this. `peer_add` additionally
|
|
supports passing the remote cluster monitor address and the user key. However, bootstrapping
|
|
a peer is the recommended way to add a peer.
|
|
|
|
.. note:: Only a single peer is supported right now.
|
|
|
|
To remove a peer use::
|
|
|
|
$ ceph fs snapshot mirror peer_remove <fs_name> <peer_uuid>
|
|
|
|
.. note:: See `Mirror Daemon Status` section on how to figure out Peer UUID.
|
|
|
|
To list file system mirror peers use::
|
|
|
|
$ ceph fs snapshot mirror peer_list <fs_name>
|
|
|
|
To configure a directory for mirroring, use::
|
|
|
|
$ ceph fs snapshot mirror add <fs_name> <path>
|
|
|
|
To stop a mirroring directory snapshots use::
|
|
|
|
$ ceph fs snapshot mirror remove <fs_name> <path>
|
|
|
|
Only absolute directory paths are allowed. Also, paths are normalized by the mirroring
|
|
module, therefore, `/a/b/../b` is equivalent to `/a/b`.
|
|
|
|
$ mkdir -p /d0/d1/d2
|
|
$ ceph fs snapshot mirror add cephfs /d0/d1/d2
|
|
{}
|
|
$ ceph fs snapshot mirror add cephfs /d0/d1/../d1/d2
|
|
Error EEXIST: directory /d0/d1/d2 is already tracked
|
|
|
|
Once a directory is added for mirroring, its subdirectory or ancestor directories are
|
|
disallowed to be added for mirroring::
|
|
|
|
$ ceph fs snapshot mirror add cephfs /d0/d1
|
|
Error EINVAL: /d0/d1 is a ancestor of tracked path /d0/d1/d2
|
|
$ ceph fs snapshot mirror add cephfs /d0/d1/d2/d3
|
|
Error EINVAL: /d0/d1/d2/d3 is a subtree of tracked path /d0/d1/d2
|
|
|
|
Commands to check directory mapping (to mirror daemons) and directory distribution are
|
|
detailed in `Mirror Daemon Status` section.
|
|
|
|
Bootstrap Peers
|
|
---------------
|
|
|
|
Adding a peer (via `peer_add`) requires the peer cluster configuration and user keyring
|
|
to be available in the primary cluster (manager host and hosts running the mirror daemon).
|
|
This can be avoided by bootstrapping and importing a peer token. Peer bootstrap involves
|
|
creating a bootstrap token on the peer cluster via::
|
|
|
|
$ ceph fs snapshot mirror peer_bootstrap create <fs_name> <client_entity> <site-name>
|
|
|
|
e.g.::
|
|
|
|
$ ceph fs snapshot mirror peer_bootstrap create backup_fs client.mirror_remote site-remote
|
|
{"token": "eyJmc2lkIjogIjBkZjE3MjE3LWRmY2QtNDAzMC05MDc5LTM2Nzk4NTVkNDJlZiIsICJmaWxlc3lzdGVtIjogImJhY2t1cF9mcyIsICJ1c2VyIjogImNsaWVudC5taXJyb3JfcGVlcl9ib290c3RyYXAiLCAic2l0ZV9uYW1lIjogInNpdGUtcmVtb3RlIiwgImtleSI6ICJBUUFhcDBCZ0xtRmpOeEFBVnNyZXozai9YYUV0T2UrbUJEZlJDZz09IiwgIm1vbl9ob3N0IjogIlt2MjoxOTIuMTY4LjAuNTo0MDkxOCx2MToxOTIuMTY4LjAuNTo0MDkxOV0ifQ=="}
|
|
|
|
`site-name` refers to a user-defined string to identify the remote filesystem. In context
|
|
of `peer_add` interface, `site-name` is the passed in `cluster` name from `remote_cluster_spec`.
|
|
|
|
Import the bootstrap token in the primary cluster via::
|
|
|
|
$ ceph fs snapshot mirror peer_bootstrap import <fs_name> <token>
|
|
|
|
e.g.::
|
|
|
|
$ ceph fs snapshot mirror peer_bootstrap import cephfs eyJmc2lkIjogIjBkZjE3MjE3LWRmY2QtNDAzMC05MDc5LTM2Nzk4NTVkNDJlZiIsICJmaWxlc3lzdGVtIjogImJhY2t1cF9mcyIsICJ1c2VyIjogImNsaWVudC5taXJyb3JfcGVlcl9ib290c3RyYXAiLCAic2l0ZV9uYW1lIjogInNpdGUtcmVtb3RlIiwgImtleSI6ICJBUUFhcDBCZ0xtRmpOeEFBVnNyZXozai9YYUV0T2UrbUJEZlJDZz09IiwgIm1vbl9ob3N0IjogIlt2MjoxOTIuMTY4LjAuNTo0MDkxOCx2MToxOTIuMTY4LjAuNTo0MDkxOV0ifQ==
|
|
|
|
Mirror Daemon Status
|
|
--------------------
|
|
|
|
Mirror daemons get asynchronously notified about changes in file system mirroring status
|
|
and/or peer updates.
|
|
|
|
CephFS mirroring module provides `mirror daemon status` interface to check mirror daemon
|
|
status::
|
|
|
|
$ ceph fs snapshot mirror daemon status
|
|
|
|
E.g::
|
|
|
|
$ ceph fs snapshot mirror daemon status | jq
|
|
[
|
|
{
|
|
"daemon_id": 284167,
|
|
"filesystems": [
|
|
{
|
|
"filesystem_id": 1,
|
|
"name": "a",
|
|
"directory_count": 1,
|
|
"peers": [
|
|
{
|
|
"uuid": "02117353-8cd1-44db-976b-eb20609aa160",
|
|
"remote": {
|
|
"client_name": "client.mirror_remote",
|
|
"cluster_name": "ceph",
|
|
"fs_name": "backup_fs"
|
|
},
|
|
"stats": {
|
|
"failure_count": 1,
|
|
"recovery_count": 0
|
|
}
|
|
}
|
|
]
|
|
}
|
|
]
|
|
}
|
|
]
|
|
|
|
An entry per mirror daemon instance is displayed along with information such as configured
|
|
peers and basic stats. For more detailed stats, use the admin socket interface as detailed
|
|
below.
|
|
|
|
CephFS mirror daemons provide admin socket commands for querying mirror status. To check
|
|
available commands for mirror status use::
|
|
|
|
$ ceph --admin-daemon /path/to/mirror/daemon/admin/socket help
|
|
{
|
|
....
|
|
....
|
|
"fs mirror status cephfs@360": "get filesystem mirror status",
|
|
....
|
|
....
|
|
}
|
|
|
|
Commands with `fs mirror status` prefix provide mirror status for mirror enabled
|
|
file systems. Note that `cephfs@360` is of format `filesystem-name@filesystem-id`.
|
|
This format is required since mirror daemons get asynchronously notified regarding
|
|
file system mirror status (A file system can be deleted and recreated with the same
|
|
name).
|
|
|
|
Right now, the command provides minimal information regarding mirror status::
|
|
|
|
$ ceph --admin-daemon /var/run/ceph/cephfs-mirror.asok fs mirror status cephfs@360
|
|
{
|
|
"rados_inst": "192.168.0.5:0/1476644347",
|
|
"peers": {
|
|
"a2dc7784-e7a1-4723-b103-03ee8d8768f8": {
|
|
"remote": {
|
|
"client_name": "client.mirror_remote",
|
|
"cluster_name": "site-a",
|
|
"fs_name": "backup_fs"
|
|
}
|
|
}
|
|
},
|
|
"snap_dirs": {
|
|
"dir_count": 1
|
|
}
|
|
}
|
|
|
|
`Peers` section in the command output above shows the peer information such as unique
|
|
peer-id (UUID) and specification. The peer-id is required to remove an existing peer
|
|
as mentioned in the `Mirror Module and Interface` section.
|
|
|
|
Command with `fs mirror peer status` prefix provide peer synchronization status. This
|
|
command is of format `filesystem-name@filesystem-id peer-uuid`::
|
|
|
|
$ ceph --admin-daemon /var/run/ceph/cephfs-mirror.asok fs mirror peer status cephfs@360 a2dc7784-e7a1-4723-b103-03ee8d8768f8
|
|
{
|
|
"/d0": {
|
|
"state": "idle",
|
|
"last_synced_snap": {
|
|
"id": 120,
|
|
"name": "snap1",
|
|
"sync_duration": 0.079997898999999997,
|
|
"sync_time_stamp": "274900.558797s"
|
|
},
|
|
"snaps_synced": 2,
|
|
"snaps_deleted": 0,
|
|
"snaps_renamed": 0
|
|
}
|
|
}
|
|
|
|
Synchronization stats such as `snaps_synced`, `snaps_deleted` and `snaps_renamed` are reset
|
|
on daemon restart and/or when a directory is reassigned to another mirror daemon (when
|
|
multiple mirror daemons are deployed).
|
|
|
|
A directory can be in one of the following states::
|
|
|
|
- `idle`: The directory is currently not being synchronized
|
|
- `syncing`: The directory is currently being synchronized
|
|
- `failed`: The directory has hit upper limit of consecutive failures
|
|
|
|
When a directory hits a configured number of consecutive synchronization failures, the
|
|
mirror daemon marks it as `failed`. Synchronization for these directories are retried.
|
|
By default, the number of consecutive failures before a directory is marked as failed
|
|
is controlled by `cephfs_mirror_max_consecutive_failures_per_directory` configuration
|
|
option (default: 10) and the retry interval for failed directories is controlled via
|
|
`cephfs_mirror_retry_failed_directories_interval` configuration option (default: 60s).
|
|
|
|
E.g., adding a regular file for synchronization would result in failed status::
|
|
|
|
$ ceph fs snapshot mirror add cephfs /f0
|
|
$ ceph --admin-daemon /var/run/ceph/cephfs-mirror.asok fs mirror peer status cephfs@360 a2dc7784-e7a1-4723-b103-03ee8d8768f8
|
|
{
|
|
"/d0": {
|
|
"state": "idle",
|
|
"last_synced_snap": {
|
|
"id": 120,
|
|
"name": "snap1",
|
|
"sync_duration": 0.079997898999999997,
|
|
"sync_time_stamp": "274900.558797s"
|
|
},
|
|
"snaps_synced": 2,
|
|
"snaps_deleted": 0,
|
|
"snaps_renamed": 0
|
|
},
|
|
"/f0": {
|
|
"state": "failed",
|
|
"snaps_synced": 0,
|
|
"snaps_deleted": 0,
|
|
"snaps_renamed": 0
|
|
}
|
|
}
|
|
|
|
This allows a user to add a non-existent directory for synchronization. The mirror daemon
|
|
would mark the directory as failed and retry (less frequently). When the directory comes
|
|
to existence, the mirror daemons would unmark the failed state upon successful snapshot
|
|
synchronization.
|
|
|
|
When mirroring is disabled, the respective `fs mirror status` command for the file system
|
|
will not show up in command help.
|
|
|
|
Mirroring module provides a couple of commands to display directory mapping and distribution
|
|
information. To check which mirror daemon a directory has been mapped to use::
|
|
|
|
$ ceph fs snapshot mirror dirmap cephfs /d0/d1/d2
|
|
{
|
|
"instance_id": "404148",
|
|
"last_shuffled": 1601284516.10986,
|
|
"state": "mapped"
|
|
}
|
|
|
|
.. note:: `instance_id` is the RADOS instance-id associated with a mirror daemon.
|
|
|
|
Other information such as `state` and `last_shuffled` are interesting when running
|
|
multiple mirror daemons.
|
|
|
|
When no mirror daemons are running the above command shows::
|
|
|
|
$ ceph fs snapshot mirror dirmap cephfs /d0/d1/d2
|
|
{
|
|
"reason": "no mirror daemons running",
|
|
"state": "stalled"
|
|
}
|
|
|
|
Signifying that no mirror daemons are running and mirroring is stalled.
|
|
|
|
Re-adding Peers
|
|
---------------
|
|
|
|
When re-adding (reassigning) a peer to a file system in another cluster, ensure that
|
|
all mirror daemons have stopped synchronization to the peer. This can be checked
|
|
via `fs mirror status` admin socket command (the `Peer UUID` should not show up
|
|
in the command output). Also, it is recommended to purge synchronized directories
|
|
from the peer before re-adding it to another file system (especially those directories
|
|
which might exist in the new primary file system). This is not required if re-adding
|
|
a peer to the same primary file system it was earlier synchronized from.
|
|
|
|
Feature Status
|
|
--------------
|
|
|
|
`cephfs-mirror` daemon is built by default (follows `WITH_CEPHFS` CMake rule).
|