Date: Sat, 5 Dec 2020 08:51:08 -0500 From: Paul Mather <paul@gromit.dlib.vt.edu> To: freebsd-questions@freebsd.org Cc: tech-lists@zyxst.net Subject: Re: effect of differing spindle speeds on prospective zfs vdevs Message-ID: <EA44E7A9-961F-4101-8FBF-8EE5E81F2E2A@gromit.dlib.vt.edu> In-Reply-To: <mailman.77.1607169601.55244.freebsd-questions@freebsd.org> References: <mailman.77.1607169601.55244.freebsd-questions@freebsd.org>
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On Fri, 4 Dec 2020 23:43:15 +0000, tech-lists <tech-lists@zyxst.net> = wrote: > Normally when making an array, I'd like to use all disks all same = speed,=20 > interface, make and model but from different batches. In this case, = I've no=20 > choice, so we have multiple 1TB disks some 7.2k some 5.4k. I've not = mixed > them like this before. >=20 > What effect would this have on the final array? Slower than if all one = or the other? > No effect? I'm expecting the fastest access will be that of the = slowest vdev. I believe you are correct in intuiting that the performance of the pool = will be influenced by the slowest devices. ZFS supports a variety of pool organisations, each with differing I/O = characteristics, so "making an array" could cover a multiplicity of = possibilities. I.e., a "JBOD" pool would have different I/O = characteristics than a RAIDZ pool. Read access would also be different = than write access, and so the use case of the pool (read-intensive or = write-intensive) would I/O speeds. (And, furthermore, small random vs. = large sequential I/O will have an impact.) IIRC, write IOPS of RAIDZ pools are limited to the IOPS of the slowest = device. > Similarly some disks block size is 512b logical/512b physical, others = are=20 > 512b logical/4096 physical, still others are 4096/4096. Any effect of > mixing hardware? I understand sfs sets its own blocksize. IIRC, ZFS pools have a single ashift for the entire pool, so you should = set it to accommodate the 4096/4096 devices to avoid performance = degradation. I believe it defaults to that now, and should auto-detect = anyway. But, in a mixed setup of vdevs like you have, you should be = using ashift=3D12. I believe having an ashift=3D9 on your mixed-drive setup would have the = biggest performance impact in terms of reducing performance. Cheers, Paul.=
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