Wednesday, November 30, 2011


If you're like me, you've spend the last year wondering why your KVM based virtualization is horribly slow when doing IO. You've tried twiddling every available option in your BIOS, you've mucked about with hdparm  and libvirt/qemu settings, and you've run more timed installs of RHEL 5 than you care to admit.

If you're also like me, you tried using ext4 instead of BTRFS to store your guest images today, and found that this resolved your issue.

The relevant bz appears to be here.

The lesson I learned today is to blame experimental or newer features before anything else (though its doubtful I'll remember this next time).


  1. Actually, I first found this in F13. I haven't used BTRFS since then because of this. I think this really sucks that even in F15, it still isn't fixed, and they keep talking about pushing BTRFS out as the default file system soon in Fedora?

  2. Have you seen this article about slow IO?

  3. @Anonymous: I have! I was running though a lot of benchmarking like that, too, assuming that could be my issue as well. but it turned out to be BTRFS. Its possible I could tune things further by adjusting the cache, but I'm happy enough where it is now.

  4. Doom:


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