Date: Mon, 15 Jun 2009 09:31:54 +0300 From: Dan Naumov <dan.naumov@gmail.com> To: Freddie Cash <fjwcash@gmail.com> Cc: FreeBSD-STABLE Mailing List <freebsd-stable@freebsd.org> Subject: Re: Does this disk/filesystem layout look sane to you? Message-ID: <cf9b1ee00906142331g1c6ccbb1w979d967b4c12fea0@mail.gmail.com> In-Reply-To: <b269bc570906141916k7bcf47b2pe87a88dde2d0a7a4@mail.gmail.com> References: <cf9b1ee00906140916n64a6c0cbr69332811bfa2aa62@mail.gmail.com> <cf9b1ee00906140917j86b1e4ev4f8e0a1fb5f6b8@mail.gmail.com> <b269bc570906141916k7bcf47b2pe87a88dde2d0a7a4@mail.gmail.com>
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The main reason for NOT using zfs directly on raw disks is the fact that you cannot replace a vdev in a pool with a smaller one, only with one of equal size or bigger. This leads to a problem: if you are a regular Joe User (and not a company buying certified hardware from a specific vendor) and want to replace one of the disks in your pool. The new 2tb disk you buy can very often be actually a few sectors smaller then the disk you are trying to replace, this in turn will lead to zfs not accepting the new disk as a replacement, because it's smaller (no matter how small). Using zfs on partitions instead and keeping a few gb unused on each disk leaves us with some room to play and be able to avoid this issue. - Dan Naumov On Mon, Jun 15, 2009 at 5:16 AM, Freddie Cash<fjwcash@gmail.com> wrote: > I don't know for sure if it's the same on FreeBSD, but on Solaris, ZFS wi= ll > disable the onboard disk cache if the vdevs are not whole disks. =A0IOW, = if > you use slices, partitions, or files, the onboard disk cache is disabled. > This can lead to poor write performance.
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