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!
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