[CentOS-virt] Confused by "qemu-img convert"

Sun Apr 24 05:49:53 UTC 2011
William Kern <wkern at pixelgate.net>

VBox 4.x is slower than 3.2.12. I can not take any
> more performance hits.  I am still on 3.2.12 for the
> same reason you are using old-out-of-date Enterprise Linux.
> 8478 corrupted the hell out of a Visual Fox Pro and
> and M$SQL 2008 database.

hmm. interesting experience you had. Sorry you had to deal with that.

We've seen some disk issues on VB on EXT4 Ubuntu Guests. None of those 
resulted in lost data because the filesystem went read-only when it had 
an issue, but that rendered the image unusable, until resolved. We were 
NOT running host I/O caching and turning that back on seems to have 
solved the problem (though thats an entirely different issue since thats 
a lot of data to be sitting around waiting for a write). Ext4 issues 
identical to what we experienced were widely reported on the Ubuntu 
lists on non-VM machines as well so we aren't yet prepared to blame VB.

We are still investigating performance. In most test cases, such as some 
LAMP stack projects VB seems quite speedy and "feels" on par with other 
VM solutions, though we haven't directly measured yet.

OTOH, we recently ran into an application where the MySQL performance 
was orders of magnitude slower than the prior VM solution where it 
resided. The app involved repeated executions of a very complex SQL 
query and the speed hit was there irregardless of the RAM and number of 
CPU's presented to the VB image, we traced and saw some sort of lock 
contention and assume disk i/o was part of the problem.

We've been impressed with VB's teleportation, the ability to use RDP to 
see whats going on, and the Xwin interface, which is more cross platform 
(for us) than the VMware solution. We are disappointed in the lack of 
readily available enterprise deployment tools.

Thanks for your feedback.