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>
next in thread | previous in thread | raw e-mail | index | archive | help
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, > interface, make and model but from different batches. In this case, I've no > choice, so we have multiple 1TB disks some 7.2k some 5.4k. I've not mixed > them like this before. > > 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 > 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=12. I believe having an ashift=9 on your mixed-drive setup would have the biggest performance impact in terms of reducing performance. Cheers, Paul.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?EA44E7A9-961F-4101-8FBF-8EE5E81F2E2A>