[CentOS-virt] xen & iSCSI

Thu Sep 24 18:34:54 UTC 2009
Daniel De Marco <ddm at bartol.udel.edu>


I'm setting up xen (on centos 5.3) and I'm facing a weird performance
issue with iSCSI.

I attach the iSCSI targets to dom0 and if I use them from dom0 I obtain
good performance with simple dd tests (~100MB/s both reading and

I then use the block devices for the domU and if I repeat the same dd
from within the domU the write performace is still good (~100MB/s), but
the read performance is cut in half (~55MB/s).

I tried changing several parameters like read_ahead and such, but I can
not obtain a good read performance in the domU.

Any idea?

Thanks, Daniel.