ZFS Poor Performance in VM - DCT Drives

[nullb]

Just wondering if there's anything obvious I'm missing here.

I've done RAIDZ at level 10, ashift 12 block is 8kb (all defaults really).

There is 4 - Samsung SSD 883 - 2 TB Drives.

VM is using host CPU with virtio block, I can't account for what's basically a /2 performance hit here.
fio tests show about the same drop as well, dd is just easier to see. These tests were ran 1hr apart so there isn't a cache build up or anything like that.

 

[Dunuin]

RAIDZ at level 10

What do yu mean by that? A raidz1 (raid5) or a striped mirror (raid10)?

virtio block

Check if virtio block supports discard. You need that for ZFS and TRIM support wasn't added to virtio block not that long ago. Not sure if PVE meanwhile supports it.

And benchmarking with "/dev/zero" isn't useful as ZFS by default will compress all blocks and zeros are highly compressible. "/dev/urandom" would be better or even better you use fio for benchmarking.