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Hyper V guest slow disk access

    Question

  • I have a Hyper V cluster(2012) with a 2012 guest running 2012 acting as my file server.

    My 2 hosts are connected to a gig switch stack which in turn is connected to my Dell MD3200i.

    My file server has a "data" disk that is a VHD(fixed) on the iSCSI storage. As is it OS(dynamic)

    I'm coping 200GB right now and only seeing data thoughtput of 8MB/sec.

    When I check perfrmance on the file server the disk queue is huge. But when I check the queue for C: on the host, which is where the cluster storage appears to sit, its got a low if not no queue.

    Also did a copy using the host and saw 58MB/sec so I'm happy the network should be able to pass the data.

    Switch CPU is at 5%

    Can anyone tell me what I'm doing wrong?

    Tuesday, August 06, 2013 8:53 PM

All replies

  • Will the same issue occurs after a reboot?

    Also you could test to boot the VM to Safe Mode only to check if the same issue still exists.


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    Thursday, August 08, 2013 1:28 PM
    Moderator
  • By testing in Safe Mode it could help confirm if it related to third party program or drivers. If there is any progress please let us know.

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    Monday, August 26, 2013 2:41 AM
    Moderator
  • Hi!

    Have you found the solution?! I have the same issue: guest OS have very slow access to its fixed-size VHDX disks: about 25 Mb/s read and 2 Mb/s write (!!!) speeds.

    While on host - speed is about 150 - 200 Mb/s.

    Monday, August 26, 2013 12:52 PM
  • Hi,

    I am in the process of investigating some performance issues myself and I have noticed that VMs that have Fixed size VHDX files are experiencing a significant performance degradation. Using SQLIO as the test base, 64K random blocks are written at 40 - 60 MB/s for fixed disks but 400 - 600 MB/s for dynamic disks. I can also reproduce this on demand by converting and compressing the fixed disks. I am trying to find information on this and why we are experiencing this problem.

    I would also add that this has been the same on an iSCSI CSV based cluster and SMB 3 share hosted VMs. Any information on this would be great. Thanks

    Dean

    Monday, October 07, 2013 6:52 AM
  • Did you find an answer - I'm having the problem as well

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    Friday, April 04, 2014 11:08 AM
  • No still have the issue and its bringing my network to a halt as its my main file server having this problem.

    I do have a ticket open with Microsoft though

    Friday, April 04, 2014 11:11 AM
  • ClusterSharedVolumes is a mount point, not the same volume as C:.  So checking the queue depth for C: didn't tell you anything about your iSCSI device.  You'll have to find the physical disk that corresponds to CSV, not to C: if you want this data.

    I would suspect that your iSCSI disk isn't giving you the throughput you need.

    Friday, April 04, 2014 8:35 PM
  • I found that change my secondary hard drives on the VMs from IDE attached VHDs to SCSI attached VHDs made a big differnce

    IDE 5MB/s

    SCSI Fixed sized VHD 15-20MB/s

    SCSI Dynamic VHD 60-70MB/s

    I have only done this on a few machines so far, but its one for others to try.

    Working on trying with more important servers next

    Wednesday, April 16, 2014 1:49 PM
  • I have an MD storage with SSD drives and experiencing the same behavior.

    SCSI Fixed sized VHDx 500-1000 IO/s
    SCSI Dynamic VHDx  40k IO/s

    Pretty weird that Dynamic disks perform better that Fixed
    and that Fixed are performing so poorly.

    Thursday, April 17, 2014 9:58 AM
  • I haven't checked the IOs can you tell me how to record that?
    Thursday, April 17, 2014 10:51 AM
  • I used SQLIO

    http://www.microsoft.com/en-us/download/details.aspx?id=20163

    Thursday, April 17, 2014 11:34 AM
  • Fixed VHD always performs better than Dynamic VHD in most scenarios by roughly 10% to 15% within the exception of 4K writes, where fixed VHD performs significantly better according to the Windows Server Performance Team Blog.

    Hyper-V and VHD Performance - Dynamic vs. Fixed:

    http://blogs.technet.com/b/winserverperformance/archive/2008/09/19/hyper-v-and-vhd-performance-dynamic-vs-fixed.aspx

    Witch doesn't match your tests, so I think you missed something in your configuration schema. Read the following guideline:

    Performance Tuning Guidelines for previous versions of Windows Server:

    http://msdn.microsoft.com/en-us/library/windows/hardware/dn529134

    Regards,


    If you found this post helpful, please give it a "Helpful" vote. If it answered your question, remember to mark it as an "Answer". This posting is provided "AS IS" with no warranties and confers no rights! Always test ANY suggestion in a test environment before implementing!

    Thursday, April 17, 2014 11:45 AM