mfschunktool(8)

NAME
mfschunktool - checks chunk integrity offline

SYNOPSIS
mfschunktool [-f] [-r] [-n] [-e] [-x] [-m damaged_dir] chunk_file|mfs_hdd_path ...

DESCRIPTION
mfschunktool checks chunk integrity using stored CRC checksums in chunk's header. It can also 'repair' chunk (fix stored checksums). This tool may be useful to check last written chunks after possible data corruption (power down etc.) If the supplied parameter is a file, the tool will check this file. If the supplied parameter is a directory, the tool will traverse this directory recursively and try to check all files that seem to be chunks (they are named like chunk files or, if -n option is used, also have headers like chunk files, even when the name is wrong).

Notice! This tool should never be used while the chunk server process is active! If the tool is used on a chunk disk (aka path in mfshdd.cfg file) it will check if the chunk server is working and refuse to operate. But if it's used on a single file or subdirectory, such check is not possible and it's the responsibility of the user to make sure the tool is not used on "working" chunks, as it could lead to data loss.

OPTIONS

-f  turn on fast mode (in this mode only last block is tested - usually this is enough to find corrupted chunks)

-r  turn on repair mode (if checksums on given chunk don't match then they will be overwritten by checksums calculated using actual data)

-n  turn on name fixing mode (if the chunk file name is not correct but there is proper file header, the tool will rename given file using data stored in the header)

-e  turn on empty block crc check for 1.0 version chunks (force checking crc values for non existing blocks - may fail in case of chunks that were truncated)

-x  turn on reporting successful check (print 'OK' message when everything is correct)

-m damaged_dir
    move damaged chunks to a specified directory damaged_dir; see NOTES

NOTES

The option to move damaged chunks to a specified directory is most useful when whole directories (disks) with chunks are scanned, and can be employed in different ways, depending on what other options are used at the same time.

If -r option is used together with -m option, then only chunks that are unrepairable will be moved. This is a fast approach to chunk repairing, that repairs and cleans the chunk directory (disk) in one go.

If only option -m is used, then all damaged chunks will be moved to a specified directory. The user can then use the mfschunktool again in this directory, this time with the -r option, to repair all chunks that can be repaired, but only introduce the repaired chunks back into the system if there is no other copy available from another chunkserver (a copy that did not need a repair operation in the first place). This is a more time consuming, but safer approach to repairing multiple chunks, e.g. after a power failure.

REPORTING BUGS
Report bugs to <bugs@moosefs.com>.

COPYRIGHT
Copyright (C) 2026 Jakub Kruszona-Zawadzki, Saglabs SA This file is part of MooseFS. MooseFS is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2 (only). MooseFS is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, see <https://www.gnu.org/licenses/>.

SEE ALSO
mfschunkserver(8)