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What are IOPs?

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Category:
ontap-9
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perf
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Applies to

All storage systems

Answer

What are the performance characteristics of different op sizes in ONTAP 9?
  • Random IOPs will take more CPU and may have higher latency than sequential
    • Random IOPs blocks are read not in any order off of disk, like block 3, 12, 66, 1, etc.
    • Sequential IOPs blocks are read in order off of disk, like block 1, 2, 3, 4, etc.
  • Smaller operation sizes generally require more computation
    • In the example above of a 1 MB file, ONTAP has to go to disk 256 times and process 256 operations at 4kB vs only 16 at 64kB
  • ONTAP will handle over 64kB fine, but due to the normalization of operation sizes, latency may appear slightly higher
    • This is better in newer versions of ONTAP 9 compared to Data ONTAP 8
    • A 1 MB read size will have 16 WAFL requests of 64kB each in parallel
Are disk IOPS measured the same as frontend IOPS?
What causes IOPS?
  • ONTAP does not track IOPS for internal processes but uses different methods of accounting them.
  • IOPS are generated from user requests for all served data protocols (CIFS/FCP/iSCSI/NFS/NVMe*/S3).
    • The only exception is if you use set advanced; statistics start -object volume -counter repl_*_ops which will show SnapMirror IOPS.
    • The commands for qos statistics and the workload objects for statistics, as well as other commands are all user IOPS.
  • If a workload burst happens, then it must be investigated from the client end.

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