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Do you know how fast your disks are?

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You really should!  For a while now I have been talking to people about how disk throughput is the most common bottleneck in private cloud deployments.  But yet most people do not know how fast their disks actually are.  To give an idea of the sort of impact disk speed can have on virtual machine performance - let me share this story:

I frequently do performance bench-marking on different builds and configurations of Hyper-V.  One of the benchmarks I do is "Windows installation time".  I have a special installation CD image that I created - which installs Windows Server 2012 R2 in a completely unattended fashion, and shuts down the virtual machine when it is completed.  Recently, I was worried that we might have introduced a significant performance regression in a daily build of Hyper-V - only to realize that I had performed my Windows installation test on a different hard disk than I usually do.  This lead to me bench marking the speeds of the different disks that I had - and performing my installation test on each configuration.

Here are the summary notes:

  • Brand new SATA3 SSD
    • Speed: ~60,000 8K IOPs
    • Windows Installation time: 3 minutes, 45 seconds
  • Two year old SATA3 SSD
    • Speed: ~15,000 8K IOPs
    • Windows installation time: 9 minutes, 50 seconds
  • RAID 10 SATA2 7,200 RPM HDD
    • Speed: ~700 8K IOPs
    • Windows installation time: 32 minutes, 25 seconds

This is quite a significant difference.  It is important to note that for these tests - all other factors (CPU, Memory, etc...) were identical.  If you have never tested the speed of your storage - Jose Barreto has a great blog post on how to do this here: https://blogs.technet.com/b/josebda/archive/2014/10/13/diskspd-powershell-and-storage-performance-measuring-iops-throughput-and-latency-for-both-local-disks-and-smb-file-shares.aspx

Cheers,

Ben

Comments

  • Anonymous
    September 16, 2015
    That big diference !! Make this test with a HD IDE too ...

  • Anonymous
    September 16, 2015
    DiskSpd is one tool, but aren't there other tools available?

  • Anonymous
    September 16, 2015
    Use Parkdale to check your disk speed: thesz.diecru.eu/.../parkdale.php

  • Anonymous
    October 05, 2015
    There are a number of tools available - I am just referring to one approach used by Jose (demigod of storage :-)

  • Anonymous
    November 04, 2015
    Nice Blog, helpfull Post ...thx :) http://welcher-computer.de

  • Anonymous
    November 22, 2015
    I always benchmark disks since it can also affect network transfer rates as well - you may have gigabit and jumbo frames but if your disks are slow you will never even pass the 100mbps rate. Quite a difference in the new Sata3 disks!

  • Anonymous
    June 22, 2016
    Feel like sharing your special CD? ;)