Lustre 1.6 Operations Manual

Additional information:
Grace period — The period of time (in seconds) within which users are allowed to
exceed their soft limit. There are four types of grace periods:
■ user block soft limit
■ user inode soft limit
■ group block soft limit
■ group inode soft limit
The grace periods are applied to all users. The user block soft limit is for all users
who are using a blocks quota.
Soft limit — Once you are beyond the soft limit, the quota module begins to time,
but you still can write block and inode. When you are always beyond the soft limit
and use up your grace time, you get the same result as the hard limit. For inodes and
blocks, it is the same. Usually, the soft limit MUST be less than the hard limit; if not,
the quota module never triggers the timing. If the soft limit is not needed, leave it as
zero (0).
Hard limit — When you are beyond the hard limit, you get -EQUOTA and cannot
write inode/block any more. The hard limit is the absolute limit. When a grace
period is set, you can exceed the soft limit within the grace period if are under the
hard limits.
Lustre quota allocation is controlled by two values quota_bunit_sz and
quota_iunit_sz referring to KBs and inodes respectively. These values can be
accessed on the MDS as /proc/fs/lustre/mds/*/quota_* and on the OST as
/proc/fs/lustre/obdfilter/*/quota_*. The /proc values are bounded by
two other variables quota_btune_sz and quota_itune_sz. By default, the
*tune_sz variables are set at 1/2 the *unit_sz variables, and you cannot set
*tune_sz larger than *unit_sz. You must set bunit_sz first if it is increasing by
more than 2x, and btune_sz first if it is decreasing by more than 2x.
Total number of inodes — To determine the total number of inodes, use lfs df -i
(and also /proc/fs/lustre/*/*/filestotal). For more information on using
the lfs df -i command and the command output, see Querying Filesystem Space.
Unfortunately, the statfs interface does not report the free inode count directly, but
instead reports the total inode and used inode counts. The free inode count is
calculated for df from (total inodes - used inodes).
It is not critical to know a filesystem’s total inode count. Instead, you should know
(accurately), the free inode count and the used inode count for a filesystem. Lustre
manipulates the total inode count in order to accurately report the other two values.
The values set for the MDS must match the values set on the OSTs.
9-8 Lustre 1.6 Operations Manual • September 2008