From owner-freebsd-stable@FreeBSD.ORG Mon Jun 15 06:31:55 2009 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 120781065677 for ; Mon, 15 Jun 2009 06:31:55 +0000 (UTC) (envelope-from dan.naumov@gmail.com) Received: from an-out-0708.google.com (an-out-0708.google.com [209.85.132.245]) by mx1.freebsd.org (Postfix) with ESMTP id BFAF38FC24 for ; Mon, 15 Jun 2009 06:31:54 +0000 (UTC) (envelope-from dan.naumov@gmail.com) Received: by an-out-0708.google.com with SMTP id c3so1895569ana.13 for ; Sun, 14 Jun 2009 23:31:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:cc:content-type :content-transfer-encoding; bh=0Sz1+T71jVdtlvO4v0ozU++rag+Un9MY7x8npQHaYOA=; b=NOoCUk+GeMulX2cEDUqQeOqZ/4BMJK8bfB1aslQt9GFVq+DeDA3sF9htsYnHmuFvx+ 1qIMYOD/unNOrPCZxV2O6To2CsS3+YRBMIf1bZFZjaUMYwqutq57pgAVUbPfVJ4pyjtk 16jL/3n5bdrf4i8MIceNJLjknwbbmfloR23nQ= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=eDXjxpqBwotLTuno7XhGcPZLlfYCMDXBrkbt/tW75OqomcLF2txF0vXodrUSNSJ6WG cPw7taZtnO8noYnv2KwNuQQkkbG6wvdOkFBgVbE/aD7qze72ITABQyezheZMMxVtjQqm yKnt34FX+7XQt9qcVlLBUlQ5NuXzr2cUPHEuk= MIME-Version: 1.0 Received: by 10.100.248.10 with SMTP id v10mr8231235anh.88.1245047514100; Sun, 14 Jun 2009 23:31:54 -0700 (PDT) In-Reply-To: References: Date: Mon, 15 Jun 2009 09:31:54 +0300 Message-ID: From: Dan Naumov To: Freddie Cash Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: FreeBSD-STABLE Mailing List Subject: Re: Does this disk/filesystem layout look sane to you? X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 15 Jun 2009 06:31:55 -0000 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 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.