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Thread: ESX5 and Opteron 6000-series

  1. #1

    ESX5 and Opteron 6000-series

    At my work we deployed a new ESX5 cluster consisting of 14 quad 6180SE servers, each with 256GB ram. Our plan is to consolidate everything on these servers - including Citrix Presentation something for around 1700 users.
    We been running the cluster for a while, and performance has been good.
    We then deployed 140 new Citrix servers on our new ESX cluster, and after a couple of hours, our users started complaining that their applications were "sluggish".
    We then run all sorts of test on network, storage and whatnot, but nothing obvious popped up. One thing looked strange to me, and that was a high cpu usage in the guests (mostly the Citrix servers), and almost ALL the cpu usage was kernel time!
    As always, antivirus and storage were blamed, but one of my colleagues called a guy he knows at VMWare, and the VMWare guy almost immediately asked: Is it AMD cpu's?
    He asked because he recently discovered that selecting "Automatic" on hardware assisted IOMMU virtualization doesn't work on AMD-cpu's - you have to force it "on" in the vsphere client.
    This is a VMWare bug, that really kills performance!
    We forced it "on" on all the guests, and volia - our cpu usage on the cluster dropped from 42% to under 13%, and our users are happy with the performance.
    Now we can run all our virtual machines on only two or perhaps three hosts - including 1700 Citrix users, some of which are pretty heavy users.
    Our storage is NFS-based, and with just two 10G-ethernet adapters, it's incredibly easy to add servers, if the need should arise.
    We also have MSSQL-servers, SAS and all kinds of stuff virtualized - it works very well, if you take the time to configure your storage and network correctly.

    Regards

    Grisen

  2. #2
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    Jun 2009
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    Do you have a link for that? I've searched the VMWare kb and come up blank. A google search comes up with only one other anecdotal reference to this as well.
    Embrace cowardice?

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