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What are IOPs?

Last Updated:

Applies to

All storage systems


  • IOPs stands for Input/output Operations Per Second, and are each SCSI command or NAS operation
  • Commonly used to measure the performance of storage
  • For read or write operations, please keep in mind they can be measured in units of bytes
    • Sometimes this is called operation or block size
    • A 1 MB file for example can be read in 256 4kB blocks, or 8 64kB blocks
      • In this example, 4kB would be 256 read IOPs, or 8 64kB read IOPs
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

Additional Information

A list of NFS and CIFS operations, and link to Wikipedia SCSI codes are on this article: What operations are categorized under Other IOPS in ONTAP?



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