RE: [Xen-devel] 2.4.29-xenU VBD performance (problem)

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> In dom0 (2.6.10-xen0), I'm able to write to lvm-volume at 35 
> - 40 MB/sec
> (megabytes per second). Measured with:
> "sync; date; dd if=/dev/zero of=/dev/vg0/lv0 bs=1024k 
> count=100; sync; date"
> 
> But, under domU (2.4.29-xenU), using that same lvm-volume as 
> VBD, I only get around 
> 10 - 12 MB/sec write performance measured in the same way.

That's very odd -- I see virtually no loss of throughput in a domU.

However, 100MB isn't really enough to get a decent measure as its likely to all 
still be in memory -- sync doesn't do what you think. I usually do measurements 
using a transfer size of 10x the memory of the system.

A couple of other things to try if you still experience poor peformance:
  * use a 2.6 domU
  * use a raw partition rather than LVM

We do most of our testing using 2.6 for everything, so its possible there a 
weird 2.4 domU to 2.6 dom0 performance bug.

Ian


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