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6962b4eb9b
Fixes: http://tracker.ceph.com/issues/22989 Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>
62 lines
2.2 KiB
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62 lines
2.2 KiB
ReStructuredText
.. _cephfs-disaster-recovery:
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Disaster recovery
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=================
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Metadata damage and repair
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--------------------------
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If a filesystem has inconsistent or missing metadata, it is considered
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*damaged*. You may find out about damage from a health message, or in some
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unfortunate cases from an assertion in a running MDS daemon.
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Metadata damage can result either from data loss in the underlying RADOS
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layer (e.g. multiple disk failures that lose all copies of a PG), or from
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software bugs.
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CephFS includes some tools that may be able to recover a damaged filesystem,
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but to use them safely requires a solid understanding of CephFS internals.
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The documentation for these potentially dangerous operations is on a
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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 filesystem 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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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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.. 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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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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::
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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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::
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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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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 filesystem and read their layouts, so the MDS must be
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up and running.
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