On 03/04/2013 07:19 PM, Samuel Winchenbach wrote: > Hi All, > > I have a cluster of three nodes set up. Live migration is accomplished via > an NFS mount over 10GigE shared by all three nodes. > > I have noticed that when a VM is brand new I am getting close to 60MB/s disk > write when using "dd if=/dev/zero of=file bs=1M count=1k conv=fdatasync". > after doing this 10s of times the perfomance of the disk seems to drop to > around 4 - 12 MB/s. > > I have also noticed that doing a live-migration causes a similar effect > immediately. > > Here is the virsh xml output of one of my VMs: > https://gist.github.com/swinchen/397fbe3bb74305064944 > > I have read several "tuning" guides and most of the suggestions seems to be > configured already (cache='none', virtio for network, disk and memballoon). > > Do you think qcow2 is causing my issue and if so is there a way to boot an > instance and override the disk format?
qcow may possibly be the issue. You could use raw disk images by setting the use_cow_images=False nova config option. The tradeoff there is slower instance start and increased (but more guaranteed) disk usage. Alternatively you could try to fallocate the disk image before running the perf test like: # get virt_size qemu-img info /var/lib/nova/instances/instance-0000002f/disk fallocate -n -l $virt_size /var/lib/nova/instances/instance-0000002f/disk There is also the possibility of adjusting nova to use preallocation=metadata on the qcow images (forfeiting CoW in the process), as discussed in "future work" at: https://blueprints.launchpad.net/nova/+spec/preallocated-images thanks, Pádraig. _______________________________________________ Mailing list: https://launchpad.net/~openstack Post to : openstack@lists.launchpad.net Unsubscribe : https://launchpad.net/~openstack More help : https://help.launchpad.net/ListHelp
