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SubjectRe: BTRFS: Unbelievably slow with kvm/qemu
On Tue, Jul 13, 2010 at 6:29 AM, Avi Kivity <> wrote:
> Btrfs is very slow on sync writes:
> 45KB/s, while 4-5MB/s traffic was actually going to the disk.  For every 4KB
> that the the application writes, 400KB+ of metadata is written.
> (It's actually worse, since it starts faster than the average and ends up
> slower than the average).
> For kvm, you can try cache=writeback or cache=unsafe and get better
> performance (though still slower than ext*).
Yeah, well I've already moved the virtual hd file to an ext3
partition, so the problem for me was actually already "solved" before
posting the first post. I posted the first message just to report the
particularly bad performances of Btrfs for this test-case, so that, if
not already known, they could be investigated and hopefully solved.

By the way, thanks to everyone who answered!

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