I have setup iSCSI targets (with open-iscsi) to dom0 (Xen 3.1), which are exported to paravirtualized guests: disk = [ ''phy:/dev/iscsi/test0,hda1,w'' ] Everything works fine, but there is huge overhead. If I write to iSCSI device in dom0 I get write speeds of about 29Mbytes/s, but if I write to /dev/hda1 in domU I only get about 14Mbytes/s. This kind of performance drop does not happen with regular disks or even NBD - they have some overhead but not 50% like I have with iSCSI. I have searched the list and I know that some people have successfully run setup similar to mine, so I''d like to ask if anyone could please share their experience and tell me if 50% performance drop is really normal. Thanks! _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Siim Vahtre wrote:> > I have setup iSCSI targets (with open-iscsi) to dom0 (Xen 3.1), which > are exported to paravirtualized guests: > > disk = [ ''phy:/dev/iscsi/test0,hda1,w'' ] > > Everything works fine, but there is huge overhead. If I write to iSCSI > device in dom0 I get write speeds of about 29Mbytes/s, but if I write > to /dev/hda1 in domU I only get about 14Mbytes/s. > > This kind of performance drop does not happen with regular disks or > even NBD - they have some overhead but not 50% like I have with iSCSI. > > I have searched the list and I know that some people have successfully > run setup similar to mine, so I''d like to ask if anyone could please > share their experience and tell me if 50% performance drop is really > normal. > > Thanks!The performance hit happens for me with local disk on Dom0 and with dedicated partitions for DomU use, and it''s even worse with file images on Dom0. I haven''t made or had the chance to use iscsi yet, since I only recently laid my hands on a GigE switch for my setup. How did you test this? And do you have good guidelines on setting up iscsi? I''m finding fairly useless directions all over the place, but no good guides for RedHat/CentOS setups. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> How did you test this?I measured sequential write performance with benchmarking utility found from DRBD source (http://svn.drbd.org/drbd/trunk/benchmark/dm.c). It is like dd but it will sync before concluding the tests.> And do you have good guidelines on setting up iscsi?No, sorry. I just googled a bit and used some random howtos. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Sun, 3 Jun 2007, Nico Kadel-Garcia wrote:> How did you test this?I measured sequential write performance with benchmarking utility found from DRBD source (http://svn.drbd.org/drbd/trunk/benchmark/dm.c). It is like dd but it will sync before concluding the tests.> And do you have good guidelines on setting up iscsi?No, sorry. I just googled a bit and used some random howtos. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users