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Thin Client and Virtual Machines Thread, Xenserver 5.5 w/ Sun 7110 NFS SR Slow writes in guest VM's in Technical; Hi All, I know that several people on here must have a similar setup and I am wondering if they ...
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    Xenserver 5.5 w/ Sun 7110 NFS SR Slow writes in guest VM's

    Hi All,

    I know that several people on here must have a similar setup and I am wondering if they experience the same behaviour or have a fix/workaround. Here is the setup/issue:

    3 Xenserver 5.5 hosts in a pool with a NFS SR hosted on the Sun 7110, when benchmarking within a guest VM Read speeds are great around 80 MB/s but write speeds are just horrible I'm lucky it I get over 10 MB/s! (see screenshot) There are numerous threads over on the Citrix forums regarding this problem but none seem to offer a solution. Is there someone out there with a similar setup that is able to test the write performace in a guest VM and post the results? Does anybody have an idea how to fix this issue? Cheers.
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    Ric_'s Avatar
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    What are you using to do your performance test? I'll happily check my setup but would prefer to use the same tool to give an accurate comparison.

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    Its just a quick and dirty benchmark program called crystal disk mark, but I have seen the same results using ATTO disk benchmark as well. If you could post your results that would be great.

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    Ric_'s Avatar
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    @buccy: You got a link?

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    Yeah sorry here Crystal Dew World

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    We have two storage pools on our 7110 - one mirrored and one double-parity raid. We're also using NFSv3 to (currently) a single XenServer 5.5 host.

    Mirrored volume: Read: 99.96 MB/s. Write: 24.65 MB/s.

    Double-parity volume: Read: 94.19 MB/s. Write: 19.82 MB/s.

    I don't know if that's "standard" for our configuration or not. If Ric_ comes back with figures twice our write speed I think ours might need investigating...

    As a comparison, my workstation SATA disk benchmarks at 60.94 MB/s read and 11.62 MB/s write.
    Last edited by webman; 11th June 2010 at 11:54 AM. Reason: Added XenServer version.

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    buccy (11th June 2010)

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    Your local results sound a bit off, my workstation gets 85.2 MB/s read and 76.82 MB/s write, I get similar results to these on a VM running on local storage. Thanks for posting your results.

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    5.6 is out, tried the upgrade? even the 5.5 sr2 (I think!) fixed alot of problems

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    I am a bit weary of upgrading to 5.6 as a number of issue's with it have been raised. I am going to setup a Openfiler box and test the performance from that, in the mean time is there anyone else who experiences slow writes in Xenserver?

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    I have done some further testing and enabled flow control on the SAN switch, this has made performance slightly worse!

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    Quote Originally Posted by buccy View Post
    I have done some further testing and enabled flow control on the SAN switch, this has made performance slightly worse!

    Really? I remember reading somewhere that flow control is considered essential for this kind of setup. I don't remember a performance hit when we enabled it I'll have to check.

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    Cookie any chance you could post some benchmark results from either Crystal Disk Mark or ATTO Disk benchmark, it would be reassuring to know if what I am experiencing is common so I can stop pulling my hair out!
    Last edited by buccy; 15th June 2010 at 04:06 PM.

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    Quote Originally Posted by buccy View Post
    Cookie any chance you could post some benchmark results from either Crystal Disk Mark or ATTO Disk benchmark, it would be reassuring to know if what I am experiencing is common so I can stop pulling my hair out!

    How was you testing? Were you just uploading data from a client to a Windows VM? I'll give it a try when I get a sec but we're using iSCSI here so it might not help.

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    iSCSI numbers would be useful also as I have begun investagating using it if I can't improve the NFS numbers. Both programs I listed just create temp files on the guest VM and are removed after the run. ATTO is lightweight and no install neccessary, so might be the best option.

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    I wonder how the SAN is affected when it's busy. I just got 94.44MB/s Read and 5MB/s Write but it was busy at the time. We are using the old iSCSI stack though, I'm planning a move to the latest release in the summer.
    Last edited by cookie_monster; 16th June 2010 at 11:29 AM.

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