Hi everybody, I got a server with CentOS 6.3 and KVM as a host and a windows 2k8 guest. The windows machine's disk performance is very poor. The windows guest uses VirtIO disk drivers, no cache and uses a LVM partition on a Raid1. atop shows 100% disk utilization as soon as the windows guest accesses the HDD, data transfers figures given are most times less than 1MB/s r/w, peaks are around 3MB/s r/w. I've run a few tests to see what's going on: Creating a 10GB test file on CentOS (guests switched off): time dd if=/dev/random of=testfile bs=1 count=0 seek=10G 0+0 records in 0+0 records out 0 bytes (0 B) copied, 5.777e-06 s, 0.0 kB/s real 0m0.001s user 0m0.000s sys 0m0.000s Create copy of test file created above: time cp testfile testfile2 real 0m3.136s user 0m0.440s sys 0m2.693s That looks ok to me. According to atop data transfer rates are between 130 and 180MB/s. Create copy of test file above while Windows guest boots up: time cp testfile testfile2 real 0m3.367s user 0m0.515s sys 0m2.826s not much different... Creating copy of test file above within the Win2k8R2 guest: Current Time: 20:12:32,41 copy testfile testfile2 1 file(s) copied Current Time: 20:22:08,64 576,23s That takes about 170 time longer than the copy unter CentOS! I've run the same test on a CentOS6.3 guest with the following results: time cp testfile testfile2 real 0m3.950s user 0m0.470s sys 0m3.383s that's almost as quick as the host... I've run these tests a few times, always giving about the same result. Why is the disk performance in the Win guest that poor? What can be done to improve things? Comments and ideas welcome! -- 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
