> On 10.08.2012 13:46, Julian price wrote: > >> I have 2 similar servers. Since upgrading one from CentOS 5.5 to 6, >> disk write performance in kvm guest VMs is much worse. >> ... >> Is this a known problem? If so, what's the cause? If not, is >> there a way to locate the problem rather than using trial and error? >> >> Thanks, >> Julian >> Nux! wrote: > How are you running KVM machines? Through libvirt? Not through libvirt, but using the qemu-kvm command. This is the full command-line (without libvirt): /usr/libexec/qemu-kvm -k en-gb -m 4096 -smp 2 -pidfile /media/archive/vm022/.vm022.pid -monitor unix:/media/archive/vm022/.vm022.monitor,server,nowait -usb -usbdevice tablet -net nic,macaddr=02:00:01:00:24:02 -net tap,script=/etc/incharge/qemu-ifup -vnc :2 -drive file=/media/vm022/hda.raw,index=0,media=disk -drive file=/media/archive/vm022/hdb.raw,index=1,media=disk -drive file=/media/archive/vm022/hdc.raw,index=2,media=disk > Have you made any changes to the cgroups? No, I never heard of cgroups until today! > What are you using as disks, raw files, lvm There are 2 physical disks in raid 1 configuration Apart from system and swap partitions, the majority of the disk is LVM Each VM has 3 virtual disk files. 1 system disk (hda), one temp disk (hdb) and one spare (hdc). All are raw format. The hda for each VM is stored in its own LVM volume, so a snapshot can be made and mirrored with minimal overhead. So the volume /media/vm022 contains one file (hda.raw) and one folder which is used by a monitoring task to check the volume hasn't gone read-only. hdb, hdc and the monitor & pid files are stored on a larger LVM volume /media/archive There was no LVM snapshot while any of the test timings were made. As there are so few files on /media/vm022, the reserved space is reduced using tune2fs -r 73134 /dev/mapper/vm-ic022 ...so the 32GB file fits into a 33GB LVM volume. (See https://www.centos.org/modules/newbb/viewtopic.php?topic_id=30854) All the above is identical on both the CentOS 5 and CentOS 6 servers, except that ext3 is used on the CentOS 5 host and ext4 on the CentOS 6 host, and the disk & raid hardware is a different brand. In all cases, the guest VM is CentOS 6.2 and uses ext4.