Hi everyone. I have an Ubuntu 10.04 domain U that has very poor performance on disk write, i.e.: domain 0: time sh -c "dd if=/dev/zero of=bigfile bs=8k count=1000 && sync" real 0m0.870s user 0m0.000s sys 0m0.012s domain U: time sh -c "dd if=/dev/zero of=bigfile bs=8k count=1000 && sync" real 0m38.944s user 0m0.004s sys 0m0.020s i.e. 38s vs 0.87s Of course, all the guest becomes unusable. The backend device is tap2:aio managing a raw img file. The domain 0 is ubuntu 12.04 (development branch) with 3.2.0-8 kernel but I also tried with ubuntu 10.04 The issue happens both in HVM and in PV guest mode While in PV mode I tried (on the PV) the following kernels: vmlinuz-2.6.32-318-ec2 vmlinuz-2.6.32-342-ec2 vmlinuz-2.6.32-36-server vmlinuz-2.6.32-37-server vmlinuz-2.6.35-020635rc1-generic vmlinuz-3.0.0-14-server but I had no luck I also tried disabling irqbalance on domU, setting elevator = noop on both dom0 and domU, settings the raid speed limit from 200000 to 50000, lowering the vcpus from 4 to 1, setting dedicated cpu to dom0 The issue is still there. Any ideas? Thanks to all. -- View this message in context: http://xen.1045712.n5.nabble.com/Domain-U-very-slow-performance-on-disk-write-tp5158578p5158578.html Sent from the Xen - User mailing list archive at Nabble.com.