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Merge pull request #51099 from zdover23/wip-doc-2023-04-16-dev-cephfs-mirroring-creating-users-command-formatting

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doc/dev: format command in cephfs-mirroring
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doc/dev/cephfs-mirroring.rst
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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.
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.
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.
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.
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.
.. 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).
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).
$ 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'
.. 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::