I have a unit that is experiencing some write bottle necks and back to back consistency points at times. I never see any of the disks busier than 60% even during the periods where I notice lots of CpfromCps.
The unit has 2 aggregates of 50 disk with a raid size of 18. 2 raid groups are full and the last only has 14 disks. Looking at a statit during normal operation The smaller raid group is not any busier than the larger rgs. (I'm going to try to get a statit while the back to back cps are occurring and see if this holds true)
During the periods of back to back cps I am seeing about 2500 writes ops and 7k read ops. This is a IBM rebranded N6240 with flexscale cards. (FAS3240)
So, the question is, I am thinking of enabling free_space_realloc on the aggregate and possibly read_realloc on the volumes. (sis is not in use on this unit)
Is there a way to measure the potential benefit of free_space_realloc, or rather how fragmented the aggregate is. I would not have expected it to be very fragmented at 60% used, but I would aslo expect to get maybe closer to 5k write ops before seeing back to back copies.
Questions, comments, warnings, random thoughts?
-JMS
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