[gpfsug-discuss] excessive lowDiskSpace events (how is threshold triggered?)

mark.bergman at uphs.upenn.edu mark.bergman at uphs.upenn.edu
Tue Feb 25 20:17:07 GMT 2014


I'm running GPFS 3.5.0.9 under Linux, and I'm seeing what seem to be an
excessive number of lowDiskSpace events on the "system" pool.

I've got an mmcallback set up, including a log report of which pool is
triggering the lowDiskSpace callback.

The part that is confusing me is that the "system" pool doesn't seem to be
above the policy thresholds.

For example, 'mmdf' shows that there is about 26% free in the 'system' pool:

-------------------------
disk                disk size  failure holds    holds                 free free
name                             group metadata data        in full blocks in fragments
--------------- ------------- -------- -------- ----- --------------------
-------------------
Disks in storage pool: system (Maximum disk size allowed is 33 TB)
dx80_rg16_vol1           546G       -1 yes      yes          125.1G ( 23%) 23.96G ( 4%) 
dx80_rg4_vol1            546G        1 yes      yes          108.1G ( 20%) 33.84G ( 6%) 
dx80_rg13_vol1           546G        1 yes      yes            109G ( 20%) 32.78G ( 6%) 
dx80_rg6_vol1            546G        1 yes      yes          104.4G ( 19%) 35.61G ( 7%) 
dx80_rg3_vol1            546G        1 yes      yes          105.6G ( 19%) 35.29G ( 6%) 
                -------------                         -------------------- -------------------
(pool total)           2.666T                                552.1G ( 20%) 161.5G ( 6%)
-------------------------


The current policy has several rules related to the "system" pool:

-------------------------
RULE 'move large files (50MB+) in the system pool to dx80_medium' MIGRATE FROM POOL 'system'
        TO POOL 'dx80_medium'
        THRESHOLD(77,70)
        LIMIT(95)
        WEIGHT(KB_ALLOCATED)
        WHERE FILE_SIZE >= 52428800

/* highest threshold = least free space, move newest files greater than 1MB */
RULE 'move files that have not been changed in 3 days from the system pool to dx80_medium' MIGRATE FROM POOL 'system'
        TO POOL 'dx80_medium'
        THRESHOLD(76,70)
        LIMIT(95)
        WEIGHT(KB_ALLOCATED)
        WHERE (DAYS(CURRENT_TIMESTAMP) - DAYS(CHANGE_TIME) > 3 )
        AND KB_ALLOCATED >= 1024

/* next threshold: some free space, move middle-aged files */
RULE 'move files that have not been changed in 7 days from the system pool to dx80_medium' MIGRATE FROM POOL 'system'
        TO POOL 'dx80_medium'
        THRESHOLD(75,65)
        LIMIT(95)
        WEIGHT(KB_ALLOCATED)
        WHERE (DAYS(CURRENT_TIMESTAMP) - DAYS(CHANGE_TIME) > 7 )
        AND KB_ALLOCATED >= 1024
-------------------------


As I understand it, none of those rules should trigger a lowDiskSpace event
when the pool is 74% full, as it is now.

Is the threshold in a file migration policy based on the %free (or used) in
full blocks only, or in the sum of full blocks plus fragments?

Thanks,

Mark




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