Hi, 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 writing). I then use the block devices for the domU and if I repeat the same dd test 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. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> I then use the block devices for the domU and if I repeat the same dd test > from within the domU the write performace is still good (~100MB/s), but > the read performance is cut in half (~55MB/s).How much memory is available to dom0? Try scaling it down to the amount available in domU. Caching will throw off i/o numbers. John -- John Madden Sr UNIX Systems Engineer Ivy Tech Community College of Indiana jmadden@ivytech.edu _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
* John Madden <jmadden@ivytech.edu> [09/24/2009 16:57]:> How much memory is available to dom0? Try scaling it down to the amount > available in domU. Caching will throw off i/o numbers.dom0 and domu are both limited to 1G. I was also watching the disk IO on the iSCSI server and the numbers were reasonably the same, so I don''t think it is caching. Doing some more tests I found another problem with this domu, the network speed with netperf is about 450Mbit/s from this domU to another machine, while it is 950Mbit/s from dom0 to the other machine. Can this be related? Thanks, Daniel. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> Doing some more tests I found another problem with this domu, the > network speed with netperf is about 450Mbit/s from this domU to another > machine, while it is 950Mbit/s from dom0 to the other machine. Can this > be related?If you''re running the iscsi initiator in domU, yes. I prefer to do it in dom0 and just pass the phy: to domU. John -- John Madden Sr UNIX Systems Engineer Ivy Tech Community College of Indiana jmadden@ivytech.edu _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
* John Madden <jmadden@ivytech.edu> [09/24/2009 17:08]:> If you''re running the iscsi initiator in domU, yes. I prefer to do it > in dom0 and just pass the phy: to domU.no, I''m running the initiator in dom0 and passing the phy to domU. weird... Daniel. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> -----Original Message----- > From: xen-users-bounces@lists.xensource.com [mailto:xen-users- > bounces@lists.xensource.com] On Behalf Of Daniel De Marco > Sent: Thursday, September 24, 2009 2:13 PM > To: xen-users@lists.xensource.com > Subject: [Xen-users] xen & iSCSI > > I attach the iSCSI targets to dom0 and if I use them from dom0 Iobtain> good performance with simple dd tests (~100MB/s both reading and > writing). > > I then use the block devices for the domU and if I repeat the same ddtest> from within the domU the write performace is still good (~100MB/s),but> the read performance is cut in half (~55MB/s).That''s odd. How many physical CPU''s (cores) do you have? How many VCPU''s have you given to dom0 and domU? Does it make any difference if you pin the dom0 VCPU, or domU VCPU, or both? -Jeff _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
* Jeff Sturm <jeff.sturm@eprize.com> [09/24/2009 17:53]:> That''s odd. > > How many physical CPU''s (cores) do you have? How many VCPU''s have you > given to dom0 and domU? > > Does it make any difference if you pin the dom0 VCPU, or domU VCPU, or > both?the machine has 8 cores and I pinned core 0 to dom0 and assigned 1 vcpu to the domU free to roam cores 1-7. Daniel. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
* Daniel De Marco <ddm@bartol.udel.edu> [09/24/2009 17:02]:> Doing some more tests I found another problem with this domu, the > network speed with netperf is about 450Mbit/s from this domU to > another > machine, while it is 950Mbit/s from dom0 to the other machine. Can > this > be related?Please disregard the network speed discrepancy. I was not comparing the same thing. Both dom0 and domU are doing 950Mbit/s, but the iSCSI part is still weird. Daniel. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users