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424 lines
16 KiB
ReStructuredText
424 lines
16 KiB
ReStructuredText
.. _cephfs-mirroring:
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=========================
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CephFS Snapshot Mirroring
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=========================
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CephFS supports asynchronous replication of snapshots to a remote CephFS file system via
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the `cephfs-mirror` tool. Snapshots are synchronized by mirroring snapshot data followed by
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creating a remote snapshot with the same name (for a given directory on the remote file system) as
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the source snapshot.
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Requirements
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------------
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The primary (local) and secondary (remote) Ceph clusters version should be Pacific or later.
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.. _cephfs_mirroring_creating_users:
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Creating Users
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--------------
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Start by creating a Ceph user (on the primary/local cluster) for the `cephfs-mirror` daemon. This user
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requires write capability on the metadata pool to create RADOS objects (index objects)
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for watch/notify operation and read capability on the data pool(s)::
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$ 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'
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Create a Ceph user for each file system peer (on the secondary/remote cluster). This user needs
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to have full capabilities on the MDS (to take snapshots) and the OSDs::
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$ ceph fs authorize <fs_name> client.mirror_remote / rwps
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This user will be supplied as part of the peer specification when adding a peer.
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Starting Mirror Daemon
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----------------------
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The mirror daemon should be spawned using `systemctl(1)` unit files::
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$ systemctl enable cephfs-mirror@mirror
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$ systemctl start cephfs-mirror@mirror
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`cephfs-mirror` daemon can be run in foreground using::
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$ cephfs-mirror --id mirror --cluster site-a -f
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.. note:: The user specified here is `mirror`, the creation of which is
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described in the :ref:`Creating Users<cephfs_mirroring_creating_users>`
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section.
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Multiple ``cephfs-mirror`` daemons may be deployed for concurrent
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synchronization and high availability. Mirror daemons share the synchronization
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load using a simple ``M/N`` policy, where ``M`` is the number of directories
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and ``N`` is the number of ``cephfs-mirror`` daemons.
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When ``cephadm`` is used to manage a Ceph cluster, ``cephfs-mirror`` daemons can be
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deployed by running the following command:
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.. prompt:: bash $
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ceph orch apply cephfs-mirror
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To deploy multiple mirror daemons, run a command of the following form:
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.. prompt:: bash $
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ceph orch apply cephfs-mirror --placement=<placement-spec>
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For example, to deploy 3 `cephfs-mirror` daemons on different hosts, run a command of the following form:
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.. prompt:: bash $
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$ ceph orch apply cephfs-mirror --placement="3 host1,host2,host3"
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Interface
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---------
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The `Mirroring` module (manager plugin) provides interfaces for managing
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directory snapshot mirroring. These are (mostly) wrappers around monitor
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commands for managing file system mirroring and is the recommended control
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interface.
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Mirroring Module
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----------------
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The mirroring module is responsible for assigning directories to mirror daemons
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for synchronization. Multiple mirror daemons can be spawned to achieve
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concurrency in directory snapshot synchronization. When mirror daemons are
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spawned (or terminated), the mirroring module discovers the modified set of
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mirror daemons and rebalances directory assignments across the new set, thus
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providing high-availability.
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.. note:: Deploying a single mirror daemon is recommended. Running multiple
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daemons is untested.
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The following file types are supported by the mirroring:
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- Regular files (-)
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- Directory files (d)
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- Symbolic link file (l)
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The other file types are ignored by the mirroring. So they won't be
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available on a successfully synchronized peer.
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The mirroring module is disabled by default. To enable the mirroring module,
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run the following command:
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.. prompt:: bash $
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ceph mgr module enable mirroring
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The mirroring module provides a family of commands that can be used to control
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the mirroring of directory snapshots. To add or remove directories, mirroring
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must be enabled for a given file system. To enable mirroring for a given file
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system, run a command of the following form:
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.. prompt:: bash $
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ceph fs snapshot mirror enable <fs_name>
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.. note:: "Mirroring module" commands are prefixed with ``fs snapshot mirror``.
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This distinguishes them from "monitor commands", which are prefixed with ``fs
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mirror``. Be sure (in this context) to use module commands.
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To disable mirroring for a given file system, run a command of the following form:
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.. prompt:: bash $
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ceph fs snapshot mirror disable <fs_name>
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After mirroring is enabled, add a peer to which directory snapshots are to be
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mirrored. Peers are specified by the ``<client>@<cluster>`` format, which is
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referred to elsewhere in this document as the ``remote_cluster_spec``. Peers
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are assigned a unique-id (UUID) when added. See the :ref:`Creating
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Users<cephfs_mirroring_creating_users>` section for instructions that describe
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how to create Ceph users for mirroring.
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To add a peer, run a command of the following form:
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.. prompt:: bash $
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ceph fs snapshot mirror peer_add <fs_name> <remote_cluster_spec> [<remote_fs_name>] [<remote_mon_host>] [<cephx_key>]
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``<remote_cluster_spec>`` is of the format ``client.<id>@<cluster_name>``.
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``<remote_fs_name>`` is optional, and defaults to `<fs_name>` (on the remote
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cluster).
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For this command to succeed, the remote cluster's Ceph configuration and user
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keyring must be available in the primary cluster. For example, if a user named
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``client_mirror`` is created on the remote cluster which has ``rwps``
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permissions for the remote file system named ``remote_fs`` (see `Creating
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Users`) and the remote cluster is named ``remote_ceph`` (that is, the remote
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cluster configuration file is named ``remote_ceph.conf`` on the primary
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cluster), run the following command to add the remote filesystem as a peer to
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the primary filesystem ``primary_fs``:
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.. prompt:: bash $
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ceph fs snapshot mirror peer_add primary_fs client.mirror_remote@remote_ceph remote_fs
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To avoid having to maintain the remote cluster configuration file and remote
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ceph user keyring in the primary cluster, users can bootstrap a peer (which
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stores the relevant remote cluster details in the monitor config store on the
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primary cluster). See the :ref:`Bootstrap
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Peers<cephfs_mirroring_bootstrap_peers>` section.
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The ``peer_add`` command supports passing the remote cluster monitor address
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and the user key. However, bootstrapping a peer is the recommended way to add a
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peer.
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.. note:: Only a single peer is currently supported.
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To remove a peer, run a command of the following form:
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.. prompt:: bash $
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ceph fs snapshot mirror peer_remove <fs_name> <peer_uuid>
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To list file system mirror peers, run a command of the following form:
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.. prompt:: bash $
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ceph fs snapshot mirror peer_list <fs_name>
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To configure a directory for mirroring, run a command of the following form:
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.. prompt:: bash $
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ceph fs snapshot mirror add <fs_name> <path>
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To stop mirroring directory snapshots, run a command of the following form:
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.. prompt:: bash $
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ceph fs snapshot mirror remove <fs_name> <path>
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Only absolute directory paths are allowed.
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Paths are normalized by the mirroring module. This means that ``/a/b/../b`` is
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equivalent to ``/a/b``. Paths always start from the CephFS file-system root and
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not from the host system mount point.
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For example::
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$ mkdir -p /d0/d1/d2
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$ ceph fs snapshot mirror add cephfs /d0/d1/d2
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{}
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$ ceph fs snapshot mirror add cephfs /d0/d1/../d1/d2
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Error EEXIST: directory /d0/d1/d2 is already tracked
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After a directory is added for mirroring, the additional mirroring of
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subdirectories or ancestor directories is disallowed::
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$ ceph fs snapshot mirror add cephfs /d0/d1
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Error EINVAL: /d0/d1 is a ancestor of tracked path /d0/d1/d2
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$ ceph fs snapshot mirror add cephfs /d0/d1/d2/d3
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Error EINVAL: /d0/d1/d2/d3 is a subtree of tracked path /d0/d1/d2
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The :ref:`Mirroring Status<cephfs_mirroring_mirroring_status>` section contains
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information about the commands for checking the directory mapping (to mirror
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daemons) and for checking the directory distribution.
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.. _cephfs_mirroring_bootstrap_peers:
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Bootstrap Peers
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---------------
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Adding a peer (via `peer_add`) requires the peer cluster configuration and user keyring
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to be available in the primary cluster (manager host and hosts running the mirror daemon).
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This can be avoided by bootstrapping and importing a peer token. Peer bootstrap involves
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creating a bootstrap token on the peer cluster via::
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$ ceph fs snapshot mirror peer_bootstrap create <fs_name> <client_entity> <site-name>
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e.g.::
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$ ceph fs snapshot mirror peer_bootstrap create backup_fs client.mirror_remote site-remote
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{"token": "eyJmc2lkIjogIjBkZjE3MjE3LWRmY2QtNDAzMC05MDc5LTM2Nzk4NTVkNDJlZiIsICJmaWxlc3lzdGVtIjogImJhY2t1cF9mcyIsICJ1c2VyIjogImNsaWVudC5taXJyb3JfcGVlcl9ib290c3RyYXAiLCAic2l0ZV9uYW1lIjogInNpdGUtcmVtb3RlIiwgImtleSI6ICJBUUFhcDBCZ0xtRmpOeEFBVnNyZXozai9YYUV0T2UrbUJEZlJDZz09IiwgIm1vbl9ob3N0IjogIlt2MjoxOTIuMTY4LjAuNTo0MDkxOCx2MToxOTIuMTY4LjAuNTo0MDkxOV0ifQ=="}
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`site-name` refers to a user-defined string to identify the remote filesystem. In context
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of `peer_add` interface, `site-name` is the passed in `cluster` name from `remote_cluster_spec`.
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Import the bootstrap token in the primary cluster via::
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$ ceph fs snapshot mirror peer_bootstrap import <fs_name> <token>
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e.g.::
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$ ceph fs snapshot mirror peer_bootstrap import cephfs eyJmc2lkIjogIjBkZjE3MjE3LWRmY2QtNDAzMC05MDc5LTM2Nzk4NTVkNDJlZiIsICJmaWxlc3lzdGVtIjogImJhY2t1cF9mcyIsICJ1c2VyIjogImNsaWVudC5taXJyb3JfcGVlcl9ib290c3RyYXAiLCAic2l0ZV9uYW1lIjogInNpdGUtcmVtb3RlIiwgImtleSI6ICJBUUFhcDBCZ0xtRmpOeEFBVnNyZXozai9YYUV0T2UrbUJEZlJDZz09IiwgIm1vbl9ob3N0IjogIlt2MjoxOTIuMTY4LjAuNTo0MDkxOCx2MToxOTIuMTY4LjAuNTo0MDkxOV0ifQ==
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.. _cephfs_mirroring_mirroring_status:
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Mirroring Status
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----------------
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CephFS mirroring module provides `mirror daemon status` interface to check mirror daemon status::
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$ ceph fs snapshot mirror daemon status
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[
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{
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"daemon_id": 284167,
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"filesystems": [
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{
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"filesystem_id": 1,
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"name": "a",
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"directory_count": 1,
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"peers": [
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{
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"uuid": "02117353-8cd1-44db-976b-eb20609aa160",
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"remote": {
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"client_name": "client.mirror_remote",
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"cluster_name": "ceph",
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"fs_name": "backup_fs"
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},
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"stats": {
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"failure_count": 1,
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"recovery_count": 0
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}
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}
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]
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}
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]
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}
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]
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An entry per mirror daemon instance is displayed along with information such as configured
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peers and basic stats. For more detailed stats, use the admin socket interface as detailed
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below.
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CephFS mirror daemons provide admin socket commands for querying mirror status. To check
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available commands for mirror status use::
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$ ceph --admin-daemon /path/to/mirror/daemon/admin/socket help
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{
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....
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....
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"fs mirror status cephfs@360": "get filesystem mirror status",
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....
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....
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}
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Commands prefixed with`fs mirror status` provide mirror status for mirror enabled
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file systems. Note that `cephfs@360` is of format `filesystem-name@filesystem-id`.
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This format is required since mirror daemons get asynchronously notified regarding
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file system mirror status (A file system can be deleted and recreated with the same
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name).
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This command currently provides minimal information regarding mirror status::
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$ ceph --admin-daemon /var/run/ceph/cephfs-mirror.asok fs mirror status cephfs@360
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{
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"rados_inst": "192.168.0.5:0/1476644347",
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"peers": {
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"a2dc7784-e7a1-4723-b103-03ee8d8768f8": {
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"remote": {
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"client_name": "client.mirror_remote",
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"cluster_name": "site-a",
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"fs_name": "backup_fs"
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}
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}
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},
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"snap_dirs": {
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"dir_count": 1
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}
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}
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The `Peers` section in the command output above shows the peer information including the unique
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peer-id (UUID) and specification. The peer-id is required when removing an existing peer
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as mentioned in the `Mirror Module and Interface` section.
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Commands prefixed with `fs mirror peer status` provide peer synchronization status. This
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command is of format `filesystem-name@filesystem-id peer-uuid`::
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$ ceph --admin-daemon /var/run/ceph/cephfs-mirror.asok fs mirror peer status cephfs@360 a2dc7784-e7a1-4723-b103-03ee8d8768f8
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{
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"/d0": {
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"state": "idle",
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"last_synced_snap": {
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"id": 120,
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"name": "snap1",
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"sync_duration": 0.079997898999999997,
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"sync_time_stamp": "274900.558797s"
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},
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"snaps_synced": 2,
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"snaps_deleted": 0,
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"snaps_renamed": 0
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}
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}
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Synchronization stats including `snaps_synced`, `snaps_deleted` and `snaps_renamed` are reset
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on daemon restart and/or when a directory is reassigned to another mirror daemon (when
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multiple mirror daemons are deployed).
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A directory can be in one of the following states::
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- `idle`: The directory is currently not being synchronized
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- `syncing`: The directory is currently being synchronized
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- `failed`: The directory has hit upper limit of consecutive failures
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When a directory experiences a configured number of consecutive synchronization failures, the
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mirror daemon marks it as `failed`. Synchronization for these directories is retried.
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By default, the number of consecutive failures before a directory is marked as failed
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is controlled by `cephfs_mirror_max_consecutive_failures_per_directory` configuration
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option (default: 10) and the retry interval for failed directories is controlled via
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`cephfs_mirror_retry_failed_directories_interval` configuration option (default: 60s).
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E.g., adding a regular file for synchronization would result in failed status::
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$ ceph fs snapshot mirror add cephfs /f0
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$ ceph --admin-daemon /var/run/ceph/cephfs-mirror.asok fs mirror peer status cephfs@360 a2dc7784-e7a1-4723-b103-03ee8d8768f8
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{
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"/d0": {
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"state": "idle",
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"last_synced_snap": {
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"id": 120,
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"name": "snap1",
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"sync_duration": 0.079997898999999997,
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"sync_time_stamp": "274900.558797s"
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},
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"snaps_synced": 2,
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"snaps_deleted": 0,
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"snaps_renamed": 0
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},
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"/f0": {
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"state": "failed",
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"snaps_synced": 0,
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"snaps_deleted": 0,
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"snaps_renamed": 0
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}
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}
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This allows a user to add a non-existent directory for synchronization. The mirror daemon
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will mark such a directory as failed and retry (less frequently). When the directory is
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created, the mirror daemon will clear the failed state upon successful synchronization.
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When mirroring is disabled, the respective `fs mirror status` command for the file system
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will not show up in command help.
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Configuration Options
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---------------------
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.. confval:: cephfs_mirror_max_concurrent_directory_syncs
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.. confval:: cephfs_mirror_action_update_interval
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.. confval:: cephfs_mirror_restart_mirror_on_blocklist_interval
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.. confval:: cephfs_mirror_max_snapshot_sync_per_cycle
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.. confval:: cephfs_mirror_directory_scan_interval
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.. confval:: cephfs_mirror_max_consecutive_failures_per_directory
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.. confval:: cephfs_mirror_retry_failed_directories_interval
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.. confval:: cephfs_mirror_restart_mirror_on_failure_interval
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.. confval:: cephfs_mirror_mount_timeout
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Re-adding Peers
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---------------
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When re-adding (reassigning) a peer to a file system in another cluster, ensure that
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all mirror daemons have stopped synchronization to the peer. This can be checked
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via `fs mirror status` admin socket command (the `Peer UUID` should not show up
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in the command output). Also, it is recommended to purge synchronized directories
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from the peer before re-adding it to another file system (especially those directories
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which might exist in the new primary file system). This is not required if re-adding
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a peer to the same primary file system it was earlier synchronized from.
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