A few days ago I moved from runing a openSuSE DomU host to the Free XenServer 5.5.0 that Citrix is offering.

I had noticed that the VMs were running very slowly. Much slower then I remembered them running on the openSuSE DomU. So I did some tests, and it came down to the  fact that hdparm -tT /dev/sda was reporting about 1-2MB/sec for the buffered disk reads. This was taken at the console of the xenserver terminal, not on a VM.

After some research, I found out that the generic IDE drivers don’t allow for UDMA to be enabled. So I did the next best thing. I had a SATA drive of similar size in another machine, and swapped the two.

Now I get about 60MB/sec buffered disk reads. That’s what it should be. And from within a VM I get about 55MB/sec, but I don’t quite believe that. Will have to do some more extensive testing with bonnie++.