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<font face="'Lucida Sans','Lucida Grande',Arial,sans-serif">On a 32bit
Windows 2008 Server guest VM on a CentOS 5 host, iometer reported a
disk write speed of 37MB/s<br>
<br>
The same VM on a CentOS 6 host reported 0.3MB/s. i.e. The VM was
unusable.<br>
<br>
Write performance in a CentOS 6 VM was also much worse, but it was
usable.<br>
(See
<a class="moz-txt-link-freetext" href="http://lists.centos.org/pipermail/centos-virt/2012-August/002961.html">http://lists.centos.org/pipermail/centos-virt/2012-August/002961.html</a>)<br>
<br>
With iometer still running in the guest, I installed tuned on the
CentOS 6 host and enabled the virtual-host profile. iometer showed the
average disk write speed increasing immediately. A fresh iometer test
reported a disk write speed of 80MB/s.<br>
<br>
I'm not sure if the tuned-adm </font><font
face="'Lucida Sans','Lucida Grande',Arial,sans-serif">virtual-host
profile </font><font
face="'Lucida Sans','Lucida Grande',Arial,sans-serif">was available in
6.0 - it may be necessary to update to get it.<br>
<a class="moz-txt-link-freetext" href="http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Power_Management_Guide/tuned-adm.html">http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Power_Management_Guide/tuned-adm.html</a><br>
<br>
Installation is quick & easy:<br>
yum install tuned<br>
tuned-adm profile virtual-host<br>
<br>
I'm surprised not to see any other posts on this subject. Maybe
there's something peculiar about my setup that caused the dreadful
write performance & tuned-adm happened to fix it. This problem has
been a real headache and I'm extremely grateful to Philip Durbin and
jimi_c for bringing the solution to my attention.<br>
<br>
The host server was rebuilt from scratch after a RAID1 simultaneous
double disk failure (happily my DR strategy worked. Have you tested
yours recently?). It appears that CentOS 6 has some different defaults
(more conservative power saving?). Maybe upgrades don't change the
defaults, so this issue only affects new CentOS 6 installs?<br>
<br>
The iometer settings were: 1000 sectors, 16 outstanding IOs, access
specification: 16k, 0%read 0%random<br>
The figures I've reported above are the 'Total MBs per second'<br>
See <a class="moz-txt-link-freetext" href="http://www.iometer.org/doc/downloads.html">http://www.iometer.org/doc/downloads.html</a><br>
<br>
In the process of researching the problem, 2 other quick & easy
optimisations came to light, each adding a few more MB/s:<br>
- Set noatime. See:
<a class="moz-txt-link-freetext" href="http://www.activoinc.com/blog/2009/08/25/setting-noatime-and-nodiratime-for-improved-disk-performance/">http://www.activoinc.com/blog/2009/08/25/setting-noatime-and-nodiratime-for-improved-disk-performance/</a><br>
<br>
- Disable Windows disk cacheing: See
<a class="moz-txt-link-freetext" href="http://pve.proxmox.com/wiki/Windows_2003_guest_best_practices">http://pve.proxmox.com/wiki/Windows_2003_guest_best_practices</a><br>
On Windows 2008: Computer Mgmt -> Disk Mgmt -> Select Drive
(system) -> properties -> Policies tab -> uncheck 'Optimize
for quick removal'<br>
<br>
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