Data ONTAP 8.1 7-Mode
Reallocation job in the
repeat state runs every day in the background without any notice and it causes an overhead on CPU and other system resources leading to unexpected performance degradation. This can be confirmed in
Perfstat. For Aggregate Reallocation (free space reallocation), a scanner called
block reallocation could be noticed in
wafl scan status -A.
Scan id Type of scan progress
1 HyA Hit Update pvbn 17423333887 (ssd block 61964287 of 146113152) 959066 bits set
34 active bitmap rearrangement fbn 242925 of 536381 w/ max_chain_len 20
47 hybrid aggregate eviction pvbn 17485602133 (DBN 2471574 of 24352192)
771 block reallocation block 1249491968 of 1326454656 (94%)
Something similar is seen from
wafl scan status for Volume Reallocation (used space reallocation). Another symptom in
perfstat is that the Disk Read/Write throughput might be a lot higher than the user protocol Read/Write, without any internal workload to explain the gap (unaligned I/O, fragmentation, Data Protection, and Dedupe/Compression might contribute to this gap).