We're running FreeBSD with VirtIO. Disk is VirtIO in the libvirt config, and shows up as a 'vtbd' device in /dev. I'm kind of stumped on where the performance discrepancy could be coming from.
Thank You, Logan Barfield Tranquil Hosting On Wed, Feb 18, 2015 at 3:23 PM, Wido den Hollander <w...@widodh.nl> wrote: > > > On 18-02-15 21:00, Logan Barfield wrote: >> Our current deployment is KVM with Ceph RBD primary storage. We have >> rbd_cache enabled, and use "cache=none" in Qemu by default. >> >> I've been running some tests to try to figure out why our write speeds >> with FreeBSD are significantly lower than Linux. I was testing both >> RBD and local SSD storage, with various cache configurations. Out of >> all of them the only one that performed close to our standard Linux >> images was local SSD, Qemu cache=writeback, FreeBSD gpt journal >> enabled. >> > > I think the main problem is that FreeBSD uses ide/scsi and Linux uses > VirtIO. > > Have you tried running FreeBSD 10 with the OS type set to Ubuntu for > example? > >> I've been reading on various lists the reasons and risks for >> cache=none vs cache=writeback: >> - cache=none: Safer for live migration >> - cache=writeback: Ceph RBD docs claim that this is required for data >> integrity when using rbd_cache >> >> From what I can tell performance is generally the same with both, >> except in the case of FreeBSD. >> >> What is the current line of thinking on this? Should be using 'none' >> or 'writeback' with RBD by default? Is 'writeback' considered safe >> for live migration? >> > > None should still be ok, since librbd does the caching. It's not Qemu > who does the caching. > > Wido
