Hi, I think DRBD *MIGHT* be Your problem anyways... Can You try repeating Your measurments with no-disk-barrier, no-disk-flushes, no-disk-drain options for Your drbd devices and report the results? nik On Mon, Mar 02, 2009 at 04:00:57PM -0500, Malinka Rellikwodahs wrote: > On Mon, Mar 2, 2009 at 15:53, Mark van Walraven <markv@xxxxxxxxxxxxxxx> wrote: > > On Mon, Mar 02, 2009 at 03:11:59PM -0500, Malinka Rellikwodahs wrote: > >> when running with a raw disk image as a file or a raw disk image on an > >> lvm vg, I'm getting very low performance on write (5-10 MB/s) however > >> when using qcow2 format disk image the write speed is much better > >> (~30MB/s), which is consistant with a very similar setup running > >> kvm-68. Unfortunately when running the test with qcow2 the system > >> becomes unresponsive for a brief time during the test. > > > >> The host is running raid5 and drbd (drive replication software), > >> however performance on the host is performaning well and avoiding the > >> drbd layer in the guest does not improve performance, but running on > >> qcow2 does. > >> > >> Any thoughts/suggestions of what could be wrong or what to do to fix this? > > > > RAID1 has *much* better write performance. With striping RAIDs, alignment > > is important. RAID controllers sometimes introduce hidden alignment > > offsets. Excessive read-ahead is a waste of time with a lot of small > > random I/O, which is what I see mostly with guests on flat disk images. > > > > With LVM, it pays to make sure the LVs are aligned to the disk. I prefer > > boundaries with multiples of at least 64-sectors, which makes the LVM > > overhead virtually disappear. I align the guest filesystems too, when > > I can. > > > > I don't think DRBD has an effect on alignment, but you might look at > > keeping the metadata on another drive. > > > > Block - rather than file - images are much faster. > > > > Hope this helps, > > It does, however unless I'm missing something the performance is being > lost not in the lvm/raid/drbd config, because I'm using the same setup > for other partitions which are used for data on the host and write > performance to those drives is just fine. > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- ------------------------------------- Nikola CIPRICH LinuxBox.cz, s.r.o. 28. rijna 168, 709 01 Ostrava tel.: +420 596 603 142 fax: +420 596 621 273 mobil: +420 777 093 799 www.linuxbox.cz mobil servis: +420 737 238 656 email servis: servis@xxxxxxxxxxx ------------------------------------- -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
