Date: Tue, 17 May 2016 22:11:23 +0100 From: Steven Hartland <steven@multiplay.co.uk> To: "Brandon J. Wandersee" <brandon.wandersee@gmail.com> Cc: Alex Tutubalin <lexa@lexa.ru>, "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org> Subject: Re: ZFS performance bottlenecks: CPU or RAM or anything else? Message-ID: <CAHEMsqZto0wD9Ko4E9YUpYvea4jM0E4f2nC1HkAwcCG=6DfX-A@mail.gmail.com> In-Reply-To: <86shxgsdzh.fsf@WorkBox.Home> 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>
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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. 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. Don't forget that while it rebalances write performance of a multi vdev raidz will be limited to the added vdev. On Tuesday, 17 May 2016, Brandon J. Wandersee <brandon.wandersee@gmail.com> wrote: > > Alex Tutubalin writes: > > > On 5/17/2016 3:29 PM, Daniel Kalchev wrote: > > > >> Not true. You can have N-way mirror and it will survive N-1 drive > failures. > > I agree, but 3-way mirror does not looks economical compared to raidz2. > > If you're already planning for multiple simultaneous drive failures, > "economical" isn't really a factor, is it? Those disks have to get > replaced regardless of the redundancy scheme you assign to them. ;) > > Whether the concern is performance or capacity, mirrors will offer the > most flexibility. Increasing either the performance or capacity of a > RAIDZ pool necessitates either replacing every disk in the pool or > doubling the number of disks in the pool, all at once. Mirrors allow you > to grow a pool and increase/decrease redundancy asymmetrically. True, > four disks in a two-mirror stripe will see you restoring a backup if one > disk from each mirror dies, but (arguably) six disks in a two-mirror > stripe offer both better redundancy and better performance. > > Speaking strictly about performance, RAIDZ performance is pretty much > fixed, while mirrored performance will (I believe) increase slightly as > you add disks and increase greatly as you add vdevs. > > -- > > :: Brandon J. Wandersee > :: brandon.wandersee@gmail.com <javascript:;> > :: -------------------------------------------------- > :: 'The best design is as little design as possible.' > :: --- Dieter Rams ---------------------------------- > _______________________________________________ > freebsd-fs@freebsd.org <javascript:;> mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-fs > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org > <javascript:;>" >
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