RE: [Xen-users] Really slow disk write on Ubuntu

[Jeff Sturm <jeff.sturm@xxxxxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-
> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of rudi
> Sent: Monday, May 24, 2010 1:27 PM
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] Really slow disk write on Ubuntu
> 
> Results were sligthly better but still far from our expectations. Disk
> writes around 10-15 MB/s.

As a data point, I logged into one of our virtual hosts and tried:

$ dd if=/dev/zero of=/var/tmp/junk oflag=direct bs=64k count=1000
1000+0 records in
1000+0 records out
65536000 bytes (66 MB) copied, 0.971217 seconds, 67.5 MB/s

$ dd if=/var/tmp/junk iflag=direct bs=64k of=/dev/null
1000+0 records in
1000+0 records out
65536000 bytes (66 MB) copied, 0.862861 seconds, 76.0 MB/s

The disk array is currently shared by 15 domU's running across 4 dom0's.
Not as fast as dedicated 15k RPM drives would be, but not bad either.
Some of my physical hosts are faster, some are slower.

> My doubt is: should we expect much better results (and by consequence,
> there is a big misconfiguration/mistake somewhere in our stack) or
these
> results are typical and unexceptional for this kind of systems?

Are you using files or direct partitions for the guest image?  What
backend driver?

-Jeff



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