Lustre 1.6 Operations Manual

In many cases, the extent of corruption is small (some unlinked files or
directories, or perhaps some parts of an inode table have been wiped out). If
there are serious filesystem problems, e2fsck may need to use a backup
superblock (reports if it does). This causes all of the "group summary"
information to be incorrect. In and of itself, this is not a serious error as this
information is redundant and e2fsck can reconstruct this data. If the primary
superblock is not valid, then there is some corruption at the start of the device
and some amount of data may be lost. The data is somewhat protected from
beginning-of-device corruption (which is one of the more common cases) because
of the large journal placed at the start of the filesystem.
The amount of time taken to run such a check is usually 4 hours for a 1 TB MDS
device or a 2 TB OST device, but varies with the number of files and the amount
of data in the filesystem. If there are severe problems with the filesystem, it can
take 8-12 hours to complete the check.
Depending on the type of corruption, it is sometimes helpful to use debugfs to
examine the filesystem directly and learn more about the corruption.
[root@mds]# script /root/debugfs.sda
[root@mds]# debugfs /dev/sda
debugfs 1.35-lfsk8 (05-Feb-2005)
debugfs> stats
{shows superblock and group summary information}
debugfs> ls
{shows directory listing}
debugfs> stat
{shows inode information for inode number }
debugfs> stat name
{shows inode information for inode "name"}
debugfs> cd dir
{change into directory "dir", "ROOT" is start of Lustre-visible namespace}
debugfs> quit
Once you have assessed the damage (possibly with the assistance of Lustre
Support, depending on the nature of the corruption), then fixing it is the next
step. Often, it is prudent to make a backup of the filesystem metadata (time and
space permitting) in case there is a problem or if it is unclear whether e2fsck will
make the correct action (in most cases it will). To make a metadata backup, run:
[root@mds]# e2image /dev/sda /bigplace/sda.e2image
Appendix D Lustre Knowledge Base D-31