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Merge pull request ceph#64604 from zdover23/wip-doc-2025-07-21-cephfs-disaster-recovery-data-pool-damage
doc/cephfs: edit disaster-recovery.rst Reviewed-by: Anthony D'Atri <[email protected]>
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doc/cephfs/disaster-recovery.rst

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@@ -22,42 +22,44 @@ separate page: :ref:`disaster-recovery-experts`.
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Data pool damage (files affected by lost data PGs)
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--------------------------------------------------
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If a PG is lost in a *data* pool, then the file system will continue
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to operate normally, but some parts of some files will simply
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be missing (reads will return zeros).
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If a PG is lost in a *data* pool, then the file system continues to operate
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normally, but some parts of some files will simply be missing (reads will
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return zeros).
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Losing a data PG may affect many files. Files are split into many objects,
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so identifying which files are affected by loss of particular PGs requires
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a full scan over all object IDs that may exist within the size of a file.
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This type of scan may be useful for identifying which files require
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restoring from a backup.
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Losing a data PG may affect many files. Files are split into many objects, so
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identifying which files have been affected by the loss of particular PGs
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requires a full scan over all object IDs that may exist within the size of a
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file. This type of scan may be useful for identifying which files must be
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restored from a backup.
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.. danger::
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This command does not repair any metadata, so when restoring files in
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this case you must *remove* the damaged file, and replace it in order
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to have a fresh inode. Do not overwrite damaged files in place.
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this case you must *remove* the damaged file and replace it in order
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to have a fresh inode. Do not overwrite damaged files in place.
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If you know that objects have been lost from PGs, use the ``pg_files``
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subcommand to scan for files that may have been damaged as a result:
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subcommand to scan for the files that may have been damaged as a result:
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::
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cephfs-data-scan pg_files <path> <pg id> [<pg id>...]
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For example, if you have lost data from PGs 1.4 and 4.5, and you would like
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to know which files under /home/bob might have been damaged:
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For example, if you have lost data from PGs 1.4 and 4.5 and you want to know
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which files under ``/home/bob`` have been damaged:
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::
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cephfs-data-scan pg_files /home/bob 1.4 4.5
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The output will be a list of paths to potentially damaged files, one
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The output is a list of paths to potentially damaged files. One file is listed
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per line.
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Note that this command acts as a normal CephFS client to find all the
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files in the file system and read their layouts, so the MDS must be
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up and running.
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.. note::
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This command acts as a normal CephFS client to find all the files in the
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file system and read their layouts. This means that the MDS must be up and
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running in order for this command to be usable.
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Using first-damage.py
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---------------------

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