HyperV HDD Performance in host very slow


  • I've been happily running HyperV on Windows Server 2008 & 2008 R2 for the last couple of years. My Servers are really big PCs, so nothing special.

    I've taken the mobo that used to be my HyperV server, and installed Windows 8 on it. It has 16GB RAM & 3.1 GHz Quad core so quite capable of running 3 or 4 VMs. This is what is was doing with Windows 2008.

    I've added HyperV role to Windows 8, and the HDD performance on the host grinds to a halt when more than 1 VM is running. Disk average throughput measured by HD Tune Pro drops from 135MB with no VM, to 44MB with 1, all the way down to 0.7 MB with 4.

    Disk Access time drops from 15.3ms to 23.8, then finally 606.8 ms.

    My new 'Server' is running the same HDD and does not show a similar drop in performance. It's happily running 6VMs.

    I think that leaves 2 possible problems: either the HDD is starting to fail, or HyperV in Windows 8 doesn't work as well as in Server 2008 R2.

    Any thoughts? Is it time to replace the HDD?




    Thursday, October 25, 2012 3:00 PM


  • Still talking to myself! I've decided to split the VMs across the 2HDDs for now, without using RAID. Hopefully, Windows 8 will have some updates to improve things shortly.

    Failing that, I'll just have to go to Windows Server 2012.


    • Marked as answer by Andrew Baines Tuesday, October 30, 2012 5:08 PM
    Tuesday, October 30, 2012 5:08 PM

All replies

  • Are both systems using the same disk controllers?  One might be more robust than the other for multi-tasking.


    Thursday, October 25, 2012 9:02 PM
  • Hi,

    Which kind of storage device are you using in the Windows 8 computer? And which kind of disk controller are you using?

    Please contact computer manufactory to get and update the latest disk controller driver.

    Use disk tool to do a health check for the disk.

    Run disk maintenance tool such as Chkdsk on the computer to detect and correct any file system errors.

    Perform disk defragmentation on the computer.

    Refer to this article to monitor disk performance and give us feedback for further troubleshooting:

    Measuring Performance on Hyper-V
    How to Monitor Disk Performance with Performance Monitor

    Hope this helps!

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    TechNet Community Support

    Friday, October 26, 2012 5:19 AM
  • Possible causes?

    1. Moved from a server OS to a client OS, there is a difference

    2. Poor pre-release drivers for Windows 8 disk controllers (remember Win8 isn't released until 10/26)

    3. Disk contention, 4 VMs is a lot to run on one spindle.  What are they doing?  Windows is very chatty with the disk...are you getting WU on all of them?  Are you also running the host OS on the same disk?  Disks are the biggest bottleneck for Hyper-V.

    4. Antivirus, did you exclude your VMs from the host OS antivirus?  If not, you should.

    Friday, October 26, 2012 5:29 AM
  • Thanks all for the rapid responses.

    The OS is on a separate drive, and the drive containing all the VMs is excluded from Anti-Virus.

    Disk Controllers are the same - I've just changed the OS from how this was setup previously.

    I'm using the release version of Windows 8 - this is from the Partner Pack.

    That leaves me Lawrence's list to check, the possibility that it's a Windows 8 issue and the possible drive failure. New drive on the way, then I'll check through the rest.

    I'll let you know how I get on.



    Sunday, October 28, 2012 1:13 PM
  • for get better performace you have to store your vhds in the drive which has configured as a raid 10.

    Darshana Jayathilake

    Sunday, October 28, 2012 4:53 PM
  • Steve - looks like it's going to be your 1, 2 or 3. Only number 3 that I can do much about though.

    I tried a new HDD, same result, so it's not the HDD failing. Interesting test was to mirror the drives and compare the response time of each drive. They were both the same, so definitely not a failing HDD.

    I'm just rearranging some stuff so that I can try RAID 0.

    There aren't any newer disk controller drivers - I'm using the latest, but they are meant for Windows 7, not sure how much difference there is.

    If RAID 0 doesn't work, I'll give Windows Server 2012 a go, and just virtualize my PC setup.


    Tuesday, October 30, 2012 7:24 AM
  • Still talking to myself! I've decided to split the VMs across the 2HDDs for now, without using RAID. Hopefully, Windows 8 will have some updates to improve things shortly.

    Failing that, I'll just have to go to Windows Server 2012.


    • Marked as answer by Andrew Baines Tuesday, October 30, 2012 5:08 PM
    Tuesday, October 30, 2012 5:08 PM
  • Did anything change when you split the disks?
    Tuesday, October 30, 2012 5:42 PM
  • No, the whole setup seems odd. I think it must be something to do with Windows 8 and its handling of hard drives.

    Even file copy is odd - if I copy one file, I get 100MB/s. If I copy several at the same time, performance just plummets. I'm pretty sure it's not the motherboard as it was fine when it ran Windows 2008.

    I'll give it a couple of months, if the drivers haven't improved, I'll go to Windows Server instead.


    Tuesday, October 30, 2012 7:20 PM
  • Hi Andrew, Just ran into the same problem and found your post. Sad that you never posted the answer. I'm thinking that maybe we made the same mistake. I added the C: drive of windows 7 as dynamic and wondering if this is causing the slow down. I have just deleted that disk as converting would have taken too long. Hopefully a fixed size disk would be faster as i noted there are 2 processes running when you use dynamic disks. One is the Windows System and the other Hyper-V engine. My thinking is that windows system keeps track of the files growth and the hyperV is accessing the file for the Guest OS. I will probably end up like you answering my own question but always useful for other people to find the solutions. Will post back with results.

    Wednesday, September 26, 2018 9:02 PM
  • Ok, judging by the speed that the fixed disk is created it appears to be the solution. I'm getting a disk write speed of 150Mbps instead of the dynamic 3Mbps. (system)

    VMWP is now writing @ 7Mbps definate improvement from 3 and the windows install is going 4x faster.

    Dynamic disk appears to add a lot of overhead on your host as they grow. This is very obvious during OS install.

    Save some tomorrow time and Add your disks as fixed size not Dynamic. Dynamic is a great feature but you are probably going to run into issues once all the vhd's grow to size.

    Side Note.

    For those that do not deal with this often if you have budget for Hardware RAID with a BBU go that route. Intel Software raid Sucks and gives more hastles than what it is worth. Great for a startup but not so great for a busy server. VMware had the right idea by only allowing Hardware raid as much as i Hate to say that it is true. Only adding this because i'm working on a server with Intel Embedded Raid and got used to Proper RAID controllers over the years. a Raid 10 Config failed completely one disk dead one with too many bad sectors so i had to restore an old 2008 VM. Not fun if you are used to the latest stuff but no budget client.

    Sorry Andrew a bit late for you but I think i solved your problem 6 years later.

    Wednesday, September 26, 2018 9:37 PM