* Brian J. Murrell <brian@xxxxxxxxxxxxxxx> [2011-12-15 15:28]: > I have a CentOS 6 host system running a CentOS 6 KVM guest and the > guest seems to get about 5x slower disk throughput than the host: > > host $ sudo dd of=/dev/datavol/disk1 if=/dev/zero bs=1M oflag=direct count=50000 > 50000+0 records in > 50000+0 records out > 52428800000 bytes (52 GB) copied, 150.36 s, 349 MB/s > host $ ssh guest dd of=/dev/vdb if=/dev/zero bs=1M oflag=direct count=50000 > 50000+0 records in > 50000+0 records out > 52428800000 bytes (52 GB) copied, 731.007 s, 71.7 MB/s > > This is actually a vast improvement over earlier tests where it was a > factor of 40x difference. But even still, I thought virtio disks were > supposed to be much closer to native host speed than 5x. --- snip --- Did you try to set the cache of the virtio disk to "none"? Regards, Stefan -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
