On 07/20/2016 02:41 AM, Marcin Falkiewicz wrote:
ZFS's zvol is really bad for virtual disk backend when you have only few HDDs (or even SSDs) - I had a lot problems with latency and throughput on my 2-disk mirrored testbench. Hard to tell if it's ZFS itself, ZoL or just not enough disks and slow controller.
I haven't had any problems with zvols on a mirror of 7200RPM drives. It's not as snappy as my SSD, for sure, but it's reasonably fast, and I haven't noticed it bogging down the host. Some things to consider: ARC size and logbias. I have 16GiB of RAM, and 8GiB goes to the VM, so I limited my ARC to 4 GiB to avoid memory pressure issues on the host. Normally it would use half of RAM, but that would make host applications have to constantly reclaim memory from the cache. Second, I have logbias=throughput on the whole pool. I do not have a ZIL. There's a few pathological cases (on the host side) where I can get my desktop to lock up for a minute or two, such as rsyncing several hundred GiB of files from the SSD, but generally the performance is better than logbias=latency (which is the default). I find there's actually less stuttering. Plus it decreases fragmentation and makes my drives quieter (less seeking).
On the other hand, LVM runs great on single SSD (directsync+native) or even RAID1 HDDs (mdadm; none+native), achieving close to bare metal performance with virtio-scsi.
Out of curiosity, are you using scsi-hd, scsi-block, or scsi-generic? -- Regards, Samuel _______________________________________________ vfio-users mailing list vfio-users@redhat.com https://www.redhat.com/mailman/listinfo/vfio-users
