Lucas Nussbaum wrote:
Hi,
I'm experiencing bad disk I/O performance using virtio disks.
I'm using Linux 2.6.29 (host & guest), kvm 84 userspace.
On the host, and in a non-virtio guest, I get ~120 MB/s when writing
with dd (the disks are fast RAID0 SAS disks).
Could you provide detail of the exact type and size
of i/o load you were creating with dd?
Also the full qemu cmd line invocation in both
cases would be useful.
In a guest with a virtio disk, I get at most ~32 MB/s.
Which non-virtio interface was used for the
comparison?
The rest of the setup is the same. For reference, I'm running kvm -drive
file=/tmp/debian-amd64.img,if=virtio.
Is such performance expected? What should I check?
Not expected, something is awry.
blktrace(8) run on the host will shed some light
on the type of i/o requests issued by qemu in both
cases.
-john
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