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https://github.com/ceph/ceph
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87215ab3e4
Fixes: https://tracker.ceph.com/issues/51459 Signed-off-by: Neeraj Pratap Singh <neesingh@redhat.com>
146 lines
4.5 KiB
ReStructuredText
146 lines
4.5 KiB
ReStructuredText
.. _mds-scrub:
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======================
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Ceph File System Scrub
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======================
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CephFS provides the cluster admin (operator) to check consistency of a file system
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via a set of scrub commands. Scrub can be classified into two parts:
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#. Forward Scrub: In which the scrub operation starts at the root of the file system
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(or a sub directory) and looks at everything that can be touched in the hierarchy
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to ensure consistency.
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#. Backward Scrub: In which the scrub operation looks at every RADOS object in the
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file system pools and maps it back to the file system hierarchy.
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This document details commands to initiate and control forward scrub (referred as
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scrub thereafter).
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.. warning::
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CephFS forward scrubs are started and manipulated on rank 0. All scrub
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commands must be directed at rank 0.
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Initiate File System Scrub
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==========================
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To start a scrub operation for a directory tree use the following command::
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ceph tell mds.<fsname>:0 scrub start <path> [scrubopts] [tag]
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where ``scrubopts`` is a comma delimited list of ``recursive``, ``force``, or
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``repair`` and ``tag`` is an optional custom string tag (the default is a generated
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UUID). An example command is::
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ceph tell mds.cephfs:0 scrub start / recursive
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{
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"return_code": 0,
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"scrub_tag": "6f0d204c-6cfd-4300-9e02-73f382fd23c1",
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"mode": "asynchronous"
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}
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Recursive scrub is asynchronous (as hinted by `mode` in the output above).
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Asynchronous scrubs must be polled using ``scrub status`` to determine the
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status.
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The scrub tag is used to differentiate scrubs and also to mark each inode's
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first data object in the default data pool (where the backtrace information is
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stored) with a ``scrub_tag`` extended attribute with the value of the tag. You
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can verify an inode was scrubbed by looking at the extended attribute using the
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RADOS utilities.
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Scrubs work for multiple active MDS (multiple ranks). The scrub is managed by
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rank 0 and distributed across MDS as appropriate.
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Monitor (ongoing) File System Scrubs
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====================================
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Status of ongoing scrubs can be monitored and polled using in `scrub status`
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command. This commands lists out ongoing scrubs (identified by the tag) along
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with the path and options used to initiate the scrub::
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ceph tell mds.cephfs:0 scrub status
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{
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"status": "scrub active (85 inodes in the stack)",
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"scrubs": {
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"6f0d204c-6cfd-4300-9e02-73f382fd23c1": {
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"path": "/",
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"options": "recursive"
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}
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}
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}
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`status` shows the number of inodes that are scheduled to be scrubbed at any point in time,
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hence, can change on subsequent `scrub status` invocations. Also, a high level summary of
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scrub operation (which includes the operation state and paths on which scrub is triggered)
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gets displayed in `ceph status`::
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ceph status
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[...]
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task status:
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scrub status:
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mds.0: active [paths:/]
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[...]
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A scrub is complete when it no longer shows up in this list (although that may
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change in future releases). Any damage will be reported via cluster health warnings.
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Control (ongoing) File System Scrubs
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====================================
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- Pause: Pausing ongoing scrub operations results in no new or pending inodes being
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scrubbed after in-flight RADOS ops (for the inodes that are currently being scrubbed)
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finish::
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ceph tell mds.cephfs:0 scrub pause
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{
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"return_code": 0
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}
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The ``scrub status`` after pausing reflects the paused state. At this point,
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initiating new scrub operations (via ``scrub start``) would just queue the
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inode for scrub::
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ceph tell mds.cephfs:0 scrub status
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{
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"status": "PAUSED (66 inodes in the stack)",
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"scrubs": {
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"6f0d204c-6cfd-4300-9e02-73f382fd23c1": {
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"path": "/",
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"options": "recursive"
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}
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}
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}
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- Resume: Resuming kick starts a paused scrub operation::
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ceph tell mds.cephfs:0 scrub resume
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{
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"return_code": 0
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}
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- Abort: Aborting ongoing scrub operations removes pending inodes from the scrub
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queue (thereby aborting the scrub) after in-flight RADOS ops (for the inodes that
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are currently being scrubbed) finish::
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ceph tell mds.cephfs:0 scrub abort
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{
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"return_code": 0
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}
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Damages
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=======
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The types of damage that can be reported and repaired by File System Scrub are:
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* DENTRY : Inode's dentry is missing.
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* DIR_FRAG : Inode's directory fragment(s) is missing.
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* BACKTRACE : Inode's backtrace in the data pool is corrupted.
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