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Is IO limit of 500 per disk is read or write or combination? RRS feed

  • Question

  • Hello,

    I'm trying to measure IO perfomance on standard disk inside Azure VM and getting vastly different numbers for performing IO tests in reads vs writes operation with caching disabled. I get full 500 IOPs on reads but only 1/10s of those for writes (50 IOPs). I'm wondering if it's expected or what could be behind this?

    G

    Thursday, January 28, 2016 9:43 PM

All replies

  • Artisticcheese,

    IO by definition means input output. So to answer, the 300 IO on basic and 500 IO on standard is a total IO passed to the disk (combination of read and write).

    Without gathering some data I cannot answer as to the cause of the issue however, I can tell you that it is not expected. Keep this in mind, where the write is coming from as bandwidth does matter on the write depending on where the write data is coming from.

    Here is how we officially define throughput:

    IO Operations are limited by either Max IOPs or the Max Read/Write throughput (MB/s), whichever they hit first (for mixed workloads a write effectively counts double against the read limit). Small IO sizes will typically max out on IOPS before hitting bandwidth limits, while large IO sizes will typically max out on bandwidth before hitting IOPS limits.

    Also by default, read/write caching is on for standard disks so you technically should be getting a bit higher than 500 iops.

    Hope that helps,

    Theo

    Friday, January 29, 2016 2:46 AM