GPFS: Administration and Programming Reference - IRA Home

Checking and repairing a file system
In general it is unnecessary to run mmfsck in offline mode unless under the direction of the IBM ®
Support
Center.
The mmfsck command finds and repairs conditions that can cause problems in your file system. The
mmfsck command operates in two modes: online and offline. The online mode operates on a mounted file
system and is chosen by issuing the -o option. Conversely, the offline mode operates on an unmounted
file system.
The online mode checks and recovers unallocated blocks on a mounted file system. If a GPFS file
operation fails due to an out of space condition, the cause may be disk blocks that have become
unavailable after repeated node failures. The corrective action taken is to mark the block free in the
allocation map. Any other inconsistencies found are only reported, not repaired.
Notes:
1. If you are running the online mmfsck command to free allocated blocks that do not belong to any files,
plan to make file system repairs when system demand is low. This is I/O intensive activity and it can
affect system performance.
2. If you are repairing a file system due to node failure and the file system has quotas enabled, it is
suggested that you run the mmcheckquota command to recreate the quota files.
To repair any other inconsistencies, you must run the offline mode of the mmfsck command on an
unmounted file system. The offline mode checks for these file inconsistencies that might cause problems:
v Blocks marked allocated that do not belong to any file. The corrective action is to mark the block free in
the allocation map.
v Files and directories for which an inode is allocated and no directory entry exists, known as orphaned
files. The corrective action is to create directory entries for these files in a lost+found subdirectory in
the root directory of the fileset to which the file or directory belongs. A fileset is a subtree of a file
system namespace that in many respects behaves like an independent file system. The index number
of the inode is assigned as the name. If you do not allow the mmfsck command to reattach an
orphaned file, it asks for permission to delete the file.
v Directory entries pointing to an inode that is not allocated. The corrective action is to remove the
directory entry.
v Incorrectly formed directory entries. A directory file contains the inode number and the generation
number of the file to which it refers. When the generation number in the directory does not match the
generation number stored in the file’s inode, the corrective action is to remove the directory entry.
v Incorrect link counts on files and directories. The corrective action is to update them with accurate
counts.
v Invalid policy files. The corrective action is to delete the file.
v Various problems related to filesets: missing or corrupted fileset metadata, inconsistencies in directory
structure related to filesets, missing or corrupted fileset root directory, other problems in internal data
structures.
The mmfsck command performs other functions not listed here, as deemed necessary by GPFS.
You cannot run the mmfsck command on a file system that has disks in a down state. You must first run
the mmchdisk command to change the state of the disks to unrecovered or up. To display the status of
the disks in the file system, issue the mmlsdisk command.
For example, to check the file system fs1 without making any changes to the file system, enter:
mmfsck fs1
The system displays information similar to:
16 GPFS: Administration and Programming Reference