On 1 May 2015 at 07:13, Nick Tan <[email protected]> wrote: > Has anyone tried using SMR disks with ZFS? I bought a Seagate 8TB SMR disk > and put it in a esata enclosure for my backups. I found that zfs send > would cause the disk to go offline. My guess is that zfs send is too fast > and fills the drive write cache.
I've been using one of those disks for about a month now with ZFS on Linux. It's part of a set of three mirror vdevs; the initial resilver took about two or three times as long as I would have expected for a traditional drive (it's hard to be sure exactly how long it would have taken with a traditional drive since my pool is a lot different compared to my last resilver: fuller and more fragmented), which if anything is better than I was expecting, since the sustained and fairly random write workload of a resilver is about the worst case scenario for an SMR drive. Since then, I've not noticed any performance issues, though the pool does not see heavy usage, and nearly never sees significant random writes. Overall, I've actually been surprised at how well it's been working: I was fully prepared for the possibility that ZFS would present a pathological use case rendering the drive almost useless, but in practice I've had no trouble at all. It is possible that Linux handles drive delays in such a way as to lower the chance of the disk going offline, although I've actually read about *more* problems with drive timeouts with ZFS on Linux than on Illumos (because there are multiple points in the stack that will wait for a timeout before reporting an error up), so I'm not sure. Currently my drive is paired with another 4TB drive, so it's effectively 100% over-provisioned. I don't think this should make a difference, but it's worth mentioning just in case. Note that the random access on-disk cache (ie, non-shingled section that acts as a persistent cache for random writes until they are written into place) is 25GB on this drive, so if you find that the first 25GB or so goes at great speed and then performance drops off a cliff and the drive starts hanging for several seconds at a time, that will be why (though I've not actually experienced any of that worst-case behaviour myself). This paper has some experimental analysis of SMR performance, specifically including measurements on the Seagate Archive drives: https://www.usenix.org/conference/fast15/technical-sessions/presentation/aghayev _______________________________________________ openindiana-discuss mailing list [email protected] http://openindiana.org/mailman/listinfo/openindiana-discuss
