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Thread: XEN hard disk performance issue

  1. #1
    Join Date
    Oct 2009
    Posts
    4

    Default XEN hard disk performance issue

    Hi,

    I'm on a Link-3 plan, XEN machine running Ubuntu-9.04 with the Redhat kernel 2.6.18-128.7.1.el5xen. df shows 25% used, free says 50-from-256Mb used. CPU+Net performance is really fine.

    Harddisk performance is really slow. Since months. AFAICR it was much faster before I moved from Seattle to NY. Yes I've read the "all to Boston" message. Here's a small bench after a reboot:

    Code:
    root@67_223_249_137:/home/sven-ola# hdparm -t -T /dev/root
    
    /dev/root:
     Timing cached reads:   3430 MB in  2.00 seconds = 1716.53 MB/sec
     Timing buffered disk reads:   12 MB in  3.03 seconds =   3.96 MB/sec
    A simple "find /etc -type f" needs 15 seconds - that's because the second value: only 3Mb/sec!?

    Is there anything I can tweak from the inside? A typical old notebook with only ~25% CPU compard to the XEN VPS shows 10 times the speed. Or am I simply on a machine with another user consuming the complete HDD bandwidth?

    // Sven-Ola

  2. #2
    Join Date
    Mar 2009
    Posts
    137

    Default

    Code:
    /dev/root:
     Timing cached reads:   9656 MB in  2.00 seconds = 4837.02 MB/sec
     Timing buffered disk reads:  968 MB in  3.00 seconds = 322.57 MB/sec
    thats what im getting on mine using the same command so it looks like someone is using alot... i would say log a ticket and see what they say

  3. #3
    Join Date
    Oct 2009
    Posts
    4

    Default

    Hey,

    thank you. That's a huge diff - let's see what a ticket can dig out.

    // Sven-Ola

  4. #4
    Join Date
    Oct 2009
    Posts
    4

    Default

    Got some emails and a professional and fast response. While my ticket description focuses on HDD bandwidth, it turns out that it was a matter of disk latency. Lots of small disk reads/writes triggered by another customers XEN guest application.

    From the perspective of a XEN guest, one may not notice any difference - you cannot hear the hard disk rattle and gasp

    My current status: every thing's back to normal currently - and I hope it stays that way...

    // Sven-Ola

  5. #5
    Join Date
    Mar 2009
    Posts
    137

    Default

    great to hear i had an issue like that on my database server a few months ago and it turned out to be the same thing and fixed by vpslink just as quick

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