mirror of
https://github.com/ceph/ceph
synced 2024-12-09 13:08:28 +00:00
a007c529e8
This is a place to put some useful notes about the new offline recovery tooling. Signed-off-by: John Spray <john.spray@redhat.com>
111 lines
3.7 KiB
ReStructuredText
111 lines
3.7 KiB
ReStructuredText
|
|
Disaster recovery
|
|
=================
|
|
|
|
.. danger::
|
|
|
|
The notes in this section are aimed at experts, making a best effort
|
|
to recovery what they can from damaged filesystems. These steps
|
|
have the potential to make things worse as well as better. If you
|
|
are unsure, do not proceed.
|
|
|
|
|
|
Journal export
|
|
--------------
|
|
|
|
Before attempting dangerous operations, make a copy of the journal like so:
|
|
|
|
::
|
|
|
|
cephfs-journal-tool journal export backup.bin
|
|
|
|
Note that this command may not always work if the journal is badly corrupted,
|
|
in which case a RADOS-level copy should be made (http://tracker.ceph.com/issues/9902).
|
|
|
|
|
|
Dentry recovery from journal
|
|
----------------------------
|
|
|
|
If a journal is damaged or for any reason an MDS is incapable of replaying it,
|
|
attempt to recover what file metadata we can like so:
|
|
|
|
::
|
|
|
|
cephfs-journal-tool event recover_dentries summary
|
|
|
|
This command by default acts on MDS rank 0, pass --rank=<n> to operate on other ranks.
|
|
|
|
This command will write any inodes/dentries recoverable from the journal
|
|
into the backing store, if these inodes/dentries are higher-versioned
|
|
than the previous contents of the backing store. If any regions of the journal
|
|
are missing/damaged, they will be skipped.
|
|
|
|
Note that in addition to writing out dentries and inodes, this command will update
|
|
the InoTables of each 'in' MDS rank, to indicate that any written inodes' numbers
|
|
are now in use. In simple cases, this will result in an entirely valid backing
|
|
store state.
|
|
|
|
.. warning::
|
|
|
|
The resulting state of the backing store is not guaranteed to be self-consistent,
|
|
and an online MDS scrub will be required afterwards. The journal contents
|
|
will not be modified by this command, you should truncate the journal
|
|
separately after recovering what you can.
|
|
|
|
Journal truncation
|
|
------------------
|
|
|
|
If the journal is corrupt or MDSs cannot replay it for any reason, you can
|
|
truncate it like so:
|
|
|
|
::
|
|
|
|
cephfs-journal-tool journal reset
|
|
|
|
.. warning::
|
|
|
|
Resetting the journal *will* lose metadata unless you have extracted
|
|
it by other means such as ``recover_dentries``. It is likely to leave
|
|
some orphaned objects in the data pool. It may result in re-allocation
|
|
of already-written inodes, such that permissions rules could be violated.
|
|
|
|
MDS table wipes
|
|
---------------
|
|
|
|
After the journal has been reset, it may no longer be consistent with respect
|
|
to the contents of the MDS tables (InoTable, SessionMap, SnapServer).
|
|
|
|
To reset the SessionMap (erase all sessions), use:
|
|
|
|
::
|
|
|
|
cephfs-table-tool all reset session
|
|
|
|
This command acts on the tables of all 'in' MDS ranks. Replace 'all' with an MDS
|
|
rank to operate on that rank only.
|
|
|
|
The session table is the table most likely to need resetting, but if you know you
|
|
also need to reset the other tables then replace 'session' with 'snap' or 'inode'.
|
|
|
|
MDS map reset
|
|
-------------
|
|
|
|
Once the in-RADOS state of the filesystem (i.e. contents of the metadata pool)
|
|
is somewhat recovered, it may be necessary to update the MDS map to reflect
|
|
the contents of the metadata pool. Use the following command to reset the MDS
|
|
map to a single MDS:
|
|
|
|
::
|
|
|
|
ceph fs reset <fs name> --yes-i-really-mean-it
|
|
|
|
Once this is run, any in-RADOS state for MDS ranks other than 0 will be ignored:
|
|
as a result it is possible for this to result in data loss.
|
|
|
|
One might wonder what the difference is between 'fs reset' and 'fs remove; fs new'. The
|
|
key distinction is that doing a remove/new will leave rank 0 in 'creating' state, such
|
|
that it would overwrite any existing root inode on disk and orphan any existing files. In
|
|
contrast, the 'reset' command will leave rank 0 in 'active' state such that the next MDS
|
|
daemon to claim the rank will go ahead and use the existing in-RADOS metadata.
|
|
|