On Fri, Jun 08, 2012 at 05:46:42PM +0100, Brian Candler wrote: > The VM boots with io='native' and bus='virtio', but performance is still > very poor: > > ubuntu at lucidtest:~$ dd if=/dev/zero of=/var/tmp/test.zeros bs=1024k count=100 > 100+0 records in > 100+0 records out > 104857600 bytes (105 MB) copied, 17.4095 s, 6.0 MB/s > > This will need some further work. And for comparison, it's not the replication which is causing the delay, because I get very similar performance if I copy the image to a distributed volume instead. This is where the VM is running on dev-storage1 but the distributed image happens to reside on dev-storage2: ubuntu at lucidtest:~$ dd if=/dev/zero of=/var/tmp/test.zeros2 bs=1024k count=100 100+0 records in 100+0 records out 104857600 bytes (105 MB) copied, 14.5182 s, 7.2 MB/s And this is after live-migrating the VM to dev-storage2: ubuntu at lucidtest:~$ dd if=/dev/zero of=/var/tmp/test.zeros3 bs=1024k count=100 100+0 records in 100+0 records out 104857600 bytes (105 MB) copied, 4.17285 s, 25.1 MB/s Clearly network latency has a part to play - this is 10GE on CAT6 (yes I know that's a poor choice for latency, but they're the NICs I happened to have spare) Given that the dd is writing large blocks, I'd hope that large ranges of blocks get flushed to disk too. Of course, 25.1 MB/s is not exactly stellar either. Maybe using a qcow2 (growable) image is part of the problem - I'll need to convert to raw and retest. Regards, Brian.
