Date: Wed, 18 May 2016 09:02:03 +0100 From: Steven Hartland <killing@multiplay.co.uk> To: freebsd-fs@freebsd.org Subject: Re: ZFS performance bottlenecks: CPU or RAM or anything else? Message-ID: <39be913e-32a5-2120-fee5-4521b8b95d80@multiplay.co.uk> In-Reply-To: <f1cc3ee5-c141-b366-83bf-3ee0179381bf@lexa.ru> References: <8441f4c0-f8d1-f540-b928-7ae60998ba8e@lexa.ru> <f87ec54a-104e-e712-7793-86c37285fdaa@internetx.com> <16e474da-6b20-2e51-9981-3c262eaff350@lexa.ru> <BD7DE274-04EB-4B19-988D-5A6FADC5B51A@digsys.bg> <1e012e43-a49b-6923-3f0a-ee77a5c8fa70@lexa.ru> <86shxgsdzh.fsf@WorkBox.Home> <CAHEMsqZto0wD9Ko4E9YUpYvea4jM0E4f2nC1HkAwcCG=6DfX-A@mail.gmail.com> <f1cc3ee5-c141-b366-83bf-3ee0179381bf@lexa.ru>
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My comment was targeted under the assumption of random IOPs workload, which is typically the case, where each RAIDZ group (vdev) will give approximately a single drive performance. For a pretty definitive guide / answer see: http://blog.delphix.com/matt/2014/06/06/zfs-stripe-width/ There's also some useful practical test results here: https://calomel.org/zfs_raid_speed_capacity.html On 18/05/2016 05:21, Alex Tutubalin wrote: > On 5/18/2016 12:11 AM, Steven Hartland wrote: >> Raidz is limited essential limited to a single drive performance per >> dev for read and write while mirror is single drive performance for >> write its number of drives for read. Don't forget mirror is not >> limited to two it can be three, four or more; so if you need more >> read throughput you can add drives to the mirror. > > Do I understand it correctly: > > - single write of one large file (or singe local write to zvol shared > via iSCSI) will be local: single or only several metaslabs > > - for RAIDZ each disk will get only part of throughput > > - for mirror, each disk included in write will receive full data size > (and for single local write only limited number of disks to be > included in write) > > If so, raidz will have huge write performance benefit in my case: > single write of one large file. > > As for read speed, I hope to deal with it with large enough L2ARC on > SSDs. > > >> >> To increase raidz performance you need to add more vdevs. While this >> doesn't have to be double i.e. the same vdev config as the first it >> generally a good idea. > > Again, multiple vdevs will help for multiple parallel writes, but not > for single one? > > Alex Tutubalin > _______________________________________________ > freebsd-fs@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-fs > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org"
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