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
