cephfs-journal-tool

Purpose

If a CephFS journal has become damaged, expert intervention may be required to restore the file system to a working state.

The cephfs-journal-tool utility provides functionality to aid experts in examining, modifying, and extracting data from journals.

Warning

This tool is dangerous because it directly modifies internal data structures of the file system. Make backups, be careful, and seek expert advice. If you are unsure, do not run this tool. As a precaution, cephfs-journal-tool doesn’t work on an active filesystem.

Syntax

cephfs-journal-tool [options] journal <inspect|import|export|reset>
cephfs-journal-tool [options] header <get|set> <trimmed_pos|expire_pos|write_pos|pool_id> <value>
cephfs-journal-tool [options] event <get|splice|recover_dentries> [filter] <list|json|summary|binary>

The tool operates in three modes: journal, header and event, meaning the whole journal, the header, and the events within the journal respectively.

Journal mode

This should be your starting point to assess the state of a journal.

inspect reports on the health of the journal. This will identify any missing objects or corruption in the stored journal. Note that this does not identify inconsistencies in the events themselves, just that events are present and can be decoded.
import and export read and write binary dumps of the journal in a sparse file format. Pass the filename as the last argument. The import operation checks if the imported journal FSID matches with the online cluster FSID. Using --force skips the FSID check. The export operation may not work reliably for journals which are damaged (missing objects).
reset truncates a journal, discarding any information within it. Using --force does a hard reset without trying to recover from on-disk.

Example: journal inspect

# cephfs-journal-tool journal inspect
Overall journal integrity: DAMAGED
Objects missing:
  0x1
Corrupt regions:
  0x400000-ffffffffffffffff

Example: Journal import/export

# cephfs-journal-tool journal export myjournal.bin
journal is 4194304~80643
read 80643 bytes at offset 4194304
wrote 80643 bytes at offset 4194304 to myjournal.bin
NOTE: this is a _sparse_ file; you can
    $ tar cSzf myjournal.bin.tgz myjournal.bin
      to efficiently compress it while preserving sparseness.

# cephfs-journal-tool journal import myjournal.bin
undump myjournal.bin
start 4194304 len 80643
writing header 200.00000000
 writing 4194304~80643
done.

Note

It is wise to use the journal export <backup file> command to make a journal backup before any further manipulation.

Header mode

get outputs the current content of the journal header
set modifies an attribute of the header. Allowed attributes are trimmed_pos, expire_pos, write_pos and pool_id.

Example: header get/set

# cephfs-journal-tool header get
{ "magic": "ceph fs volume v011",
  "write_pos": 4274947,
  "expire_pos": 4194304,
  "trimmed_pos": 4194303,
  "stream_format": 1,
  "layout": { "stripe_unit": 4194304,
      "stripe_count": 1,
      "object_size": 4194304,
      "pool_id": 2,
      "pool_ns": ""}}

# cephfs-journal-tool header set trimmed_pos 4194303
Updating trimmed_pos 0x400000 -> 0x3fffff
Successfully updated header.

Event mode

Event mode allows detailed examination and manipulation of the contents of the journal. Event mode can operate on all events in the journal, or filters may be applied.

The arguments following cephfs-journal-tool event consist of an action, optional filter parameters, and an output mode:

cephfs-journal-tool event <action> [filter] <output>

Actions:

get read the events from the log
splice erase events or regions in the journal
recover_dentries recover the dentries from the journal. It does a selective offline replay which only reads out dentries and writes them to the backing store if their version is greater than what is currently in the backing store.

Filtering:

--range <int begin>..[int end] only include events within the range begin (inclusive) to end (exclusive)
--path <path substring> only include events referring to metadata containing the specified string
--inode <int> only include events referring to metadata containing the specified inode
--type <type string> only include events of this type
--frag <ino>[.frag id] only include events referring to this directory fragment
--dname <string> only include events referring to this named dentry within a directory fragment (may only be used in conjunction with --frag
--client <int> only include events from this client session ID

Filters may be combined on an AND basis (i.e. only the intersection of events from each filter).

Output modes:

binary: write each event as a binary file, within a folder whose name is controlled by --path
json: write all events to a single file specified by --path, as a JSON serialized list of objects.
summary: write a human readable summary of the events read to standard out
list: write a human readable terse listing of the type of each event, and which file paths the event affects.

Example: event mode

# cephfs-journal-tool event get json --path output.json
Wrote output to JSON file 'output.json'

# cephfs-journal-tool event get summary
Events by type:
  NOOP: 2
  OPEN: 2
  SESSION: 2
  SUBTREEMAP: 1
  UPDATE: 43

# cephfs-journal-tool event get list
0x400000 SUBTREEMAP:  ()
0x400308 SESSION:  ()
0x4003de UPDATE:  (setattr)
  /
0x40068b UPDATE:  (mkdir)
  diralpha
0x400d1b UPDATE:  (mkdir)
  diralpha/filealpha1
0x401666 UPDATE:  (unlink_local)
  stray0/10000000001
  diralpha/filealpha1
0x40228d UPDATE:  (unlink_local)
  diralpha
  stray0/10000000000
0x402bf9 UPDATE:  (scatter_writebehind)
  stray0
0x403150 UPDATE:  (mkdir)
  dirbravo
0x4037e0 UPDATE:  (openc)
  dirbravo/.filebravo1.swp
0x404032 UPDATE:  (openc)
  dirbravo/.filebravo1.swpx

# cephfs-journal-tool event get --path filebravo1 list
0x40785a UPDATE:  (openc)
  dirbravo/filebravo1
0x4103ee UPDATE:  (cap update)
  dirbravo/filebravo1

# cephfs-journal-tool event splice --range 0x40f754..0x410bf1 summary
Events by type:
  OPEN: 1
  UPDATE: 2

# cephfs-journal-tool event recover_dentries summary
Events by type:
  LID: 1
  SUBTREEMAP: 1
Errors: 0

# cephfs-journal-tool event get --inode=1099511627776 list
0x40068b UPDATE:  (mkdir)
  diralpha
0x400d1b UPDATE:  (mkdir)
  diralpha/filealpha1
0x401666 UPDATE:  (unlink_local)
  stray0/10000000001
  diralpha/filealpha1
0x40228d UPDATE:  (unlink_local)
  diralpha
  stray0/10000000000

# cephfs-journal-tool event get --frag=1099511627776 --dname=filealpha1 list
0x400d1b UPDATE:  (mkdir)
  diralpha/filealpha1
0x401666 UPDATE:  (unlink_local)
  stray0/10000000001
  diralpha/filealpha1

# cephfs-journal-tool event get binary --path bin_events
Wrote output to binary files in directory 'bin_events'

Options

--rank=<filesystem>:{mds-rank|all} Used to specify the filesystem, the MDS rank or all ranks.
--journal=<mdlog|purge_queue> The journal type. The default value is mdlog, which is the only option that supports event mode. When purge_queue is used, the journal scanner creates a PurgeItem object and adds it to EventMap for processing.

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