Re: Disk I/O slowness

Hi,

On Fri, Jul 31, 2026 at 09:59:54AM -0500, nwe wrote:
> If your disks are SMR type then you might want to avoid ZFS. I think
> eventually, newer SMR disks will play nicer with ZFS than the first
> generations did. Maybe they're already there, I haven't followed SMR news
> recently.

I think it is more likely that *ZFS* will end up able to play nicer with
SMR disks, by altering (lowering) its expectations and specifically
catering to devices with pitiful random write performance! There's very
little motivation for manufacturers of SMR drives to make them work
better in ZFS and RAID setups because their target market is
desktop/laptop users. They'd much rather sell their more expensive
enterprise models! But as far as I understand there is some interest in
making ZFS work better with weird storage backends like SMR and even
remote block storage (e.g. S3-compatible).

With ZFS you can already get some way by putting the ZFS intent log
(ZIL) on a pair of fast power-loss-protected storage like (part of)
decent NVMe drives, then forcing all writes to be sync so they go
through the ZIL, only hitting the slow storage as streaming writes at 5
second intervals. That's a bit like what the non-volatile write cache is
doing in a hardware RAID HBA. We still can't get away from the fact that
even streaming sequential writes are slow on SMR drives though.

There aren't any good software solutions for this outside of ZFS at the
moment as far as I have found. lvmcache exists but hasn't seen
development in ages, was really clunky and underwhelming when I last
tried it. I had some hopes for bcachefs.

Thanks,
Andy