KVM slow guest i/o

Posted by Akarot on Server Fault See other posts from Server Fault or by Akarot
Published on 2012-06-01T01:42:02Z Indexed on 2012/06/01 4:43 UTC
Read the original article Hit count: 652

Filed under:

linux

|

debian

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virtualization

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kvm-virtualization

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libvirt

Host:

Debian 6.0 (squeeze) with qemu-kvm and libvirt from squeeze-backports

ii qemu-kvm 1.0+dfsg-8~bpo60+1

ii libvirt-bin 0.9.8-2~bpo60+2

Has 3TB sata drives with software raid and lvm. It has a sequential write speed of ~140MB/s measured with dd bs=1M count=512 if=/dev/zero of=test conv=fdatasync

Elevator set to cfq

Guest

Debian 6.0 (squeeze)

Uses LVM as storage. Drivers are virtio and cache='none'

Sequential write speed is considerably slower with only 25-50MB/s

Elevator set to noop

I'm kind of running out of ideas for further tweaks but I'm sure that I/O speed should be much faster because many people are reporting almost native performance with lvm.

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