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diff --git a/doc/cephfs/cephfs-mirroring.rst b/doc/cephfs/cephfs-mirroring.rst new file mode 100644 index 000000000..fd00a1eef --- /dev/null +++ b/doc/cephfs/cephfs-mirroring.rst @@ -0,0 +1,414 @@ +.. _cephfs-mirroring: + +========================= +CephFS Snapshot Mirroring +========================= + +CephFS supports asynchronous replication of snapshots to a remote CephFS file system via +the `cephfs-mirror` tool. Snapshots are synchronized by mirroring snapshot data followed by +creating a remote snapshot with the same name (for a given directory on the remote file system) as +the source snapshot. + +Requirements +------------ + +The primary (local) and secondary (remote) Ceph clusters version should be Pacific or later. + +.. _cephfs_mirroring_creating_users: + +Creating Users +-------------- + +Start by creating a Ceph user (on the primary/local cluster) for the `cephfs-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):: + + $ 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 Ceph 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 will be supplied as part of the peer specification when adding a peer. + +Starting Mirror Daemon +---------------------- + +The 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:: The user specified here is `mirror`, the creation of which is + described in the :ref:`Creating Users<cephfs_mirroring_creating_users>` + section. + +Multiple ``cephfs-mirror`` daemons may be deployed for concurrent +synchronization and high availability. Mirror daemons share the synchronization +load using a simple ``M/N`` policy, where ``M`` is the number of directories +and ``N`` is the number of ``cephfs-mirror`` daemons. + +When ``cephadm`` is used to manage a Ceph cluster, ``cephfs-mirror`` daemons can be +deployed by running the following command: + +.. prompt:: bash $ + + ceph orch apply cephfs-mirror + +To deploy multiple mirror daemons, run a command of the following form: + +.. prompt:: bash $ + + ceph orch apply cephfs-mirror --placement=<placement-spec> + +For example, to deploy 3 `cephfs-mirror` daemons on different hosts, run a command of the following form: + +.. prompt:: bash $ + + $ ceph orch apply cephfs-mirror --placement="3 host1,host2,host3" + +Interface +--------- + +The `Mirroring` module (manager plugin) provides interfaces for managing +directory snapshot mirroring. These are (mostly) wrappers around monitor +commands for managing file system mirroring and is the recommended control +interface. + +Mirroring Module +---------------- + +The mirroring 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 directory assignments across the new set, thus +providing high-availability. + +.. note:: Deploying a single mirror daemon is recommended. Running multiple + daemons is untested. + +The mirroring module is disabled by default. To enable the mirroring module, +run the following command: + +.. prompt:: bash $ + + ceph mgr module enable mirroring + +The mirroring module provides a family of commands that can be used to control +the mirroring of directory snapshots. To add or remove directories, mirroring +must be enabled for a given file system. To enable mirroring for a given file +system, run a command of the following form: + +.. prompt:: bash $ + + ceph fs snapshot mirror enable <fs_name> + +.. note:: "Mirroring module" commands are prefixed with ``fs snapshot mirror``. + This distinguishes them from "monitor commands", which are prefixed with ``fs + mirror``. Be sure (in this context) to use module commands. + +To disable mirroring for a given file system, run a command of the following form: + +.. prompt:: bash $ + + ceph fs snapshot mirror disable <fs_name> + +After mirroring is enabled, add a peer to which directory snapshots are to be +mirrored. Peers are specified by the ``<client>@<cluster>`` format, which is +referred to elsewhere in this document as the ``remote_cluster_spec``. Peers +are assigned a unique-id (UUID) when added. See the :ref:`Creating +Users<cephfs_mirroring_creating_users>` section for instructions that describe +how to create Ceph users for mirroring. + +To add a peer, run a command of the following form: + +.. prompt:: bash $ + + ceph fs snapshot mirror peer_add <fs_name> <remote_cluster_spec> [<remote_fs_name>] [<remote_mon_host>] [<cephx_key>] + +``<remote_cluster_spec>`` is of the format ``client.<id>@<cluster_name>``. + +``<remote_fs_name>`` is optional, and defaults to `<fs_name>` (on the remote +cluster). + +For this command to succeed, the remote cluster's Ceph configuration and user +keyring must be available in the primary cluster. For example, if a user named +``client_mirror`` is created on the remote cluster which has ``rwps`` +permissions for the remote file system named ``remote_fs`` (see `Creating +Users`) and the remote cluster is named ``remote_ceph`` (that is, the remote +cluster configuration file is named ``remote_ceph.conf`` on the primary +cluster), run the following command to add the remote filesystem as a peer to +the primary filesystem ``primary_fs``: + +.. prompt:: bash $ + + ceph fs snapshot mirror peer_add primary_fs client.mirror_remote@remote_ceph remote_fs + +To avoid having to maintain the remote cluster configuration file and remote +ceph user keyring in the primary cluster, users can bootstrap a peer (which +stores the relevant remote cluster details in the monitor config store on the +primary cluster). See the :ref:`Bootstrap +Peers<cephfs_mirroring_bootstrap_peers>` section. + +The ``peer_add`` command 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 currently supported. + +To remove a peer, run a command of the following form: + +.. prompt:: bash $ + + ceph fs snapshot mirror peer_remove <fs_name> <peer_uuid> + +To list file system mirror peers, run a command of the following form: + +.. prompt:: bash $ + + ceph fs snapshot mirror peer_list <fs_name> + +To configure a directory for mirroring, run a command of the following form: + +.. prompt:: bash $ + + ceph fs snapshot mirror add <fs_name> <path> + +To stop mirroring directory snapshots, run a command of the following form: + +.. prompt:: bash $ + + ceph fs snapshot mirror remove <fs_name> <path> + +Only absolute directory paths are allowed. + +Paths are normalized by the mirroring module. This means that ``/a/b/../b`` is +equivalent to ``/a/b``. Paths always start from the CephFS file-system root and +not from the host system mount point. + +For example:: + + $ 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 + +After a directory is added for mirroring, the additional mirroring of +subdirectories or ancestor directories is disallowed:: + + $ 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 + +The :ref:`Mirroring Status<cephfs_mirroring_mirroring_status>` section contains +information about the commands for checking the directory mapping (to mirror +daemons) and for checking the directory distribution. + +.. _cephfs_mirroring_bootstrap_peers: + +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== + + +.. _cephfs_mirroring_mirroring_status: + +Mirroring Status +---------------- + +CephFS mirroring module provides `mirror daemon status` interface to check mirror daemon status:: + + $ ceph fs snapshot mirror daemon status + [ + { + "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 prefixed with`fs mirror status` 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). + +This command currently 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 + } + } + +The `Peers` section in the command output above shows the peer information including the unique +peer-id (UUID) and specification. The peer-id is required when removing an existing peer +as mentioned in the `Mirror Module and Interface` section. + +Commands prefixed with `fs mirror peer status` 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 including `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 experiences a configured number of consecutive synchronization failures, the +mirror daemon marks it as `failed`. Synchronization for these directories is 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 +will mark such a directory as failed and retry (less frequently). When the directory is +created, the mirror daemon will clear the failed state upon successful synchronization. + +When mirroring is disabled, the respective `fs mirror status` command for the file system +will not show up in command help. + +Configuration Options +--------------------- + +.. confval:: cephfs_mirror_max_concurrent_directory_syncs +.. confval:: cephfs_mirror_action_update_interval +.. confval:: cephfs_mirror_restart_mirror_on_blocklist_interval +.. confval:: cephfs_mirror_max_snapshot_sync_per_cycle +.. confval:: cephfs_mirror_directory_scan_interval +.. confval:: cephfs_mirror_max_consecutive_failures_per_directory +.. confval:: cephfs_mirror_retry_failed_directories_interval +.. confval:: cephfs_mirror_restart_mirror_on_failure_interval +.. confval:: cephfs_mirror_mount_timeout + +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. |