From owner-freebsd-questions@FreeBSD.ORG Thu Nov 24 19:29:43 2011 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 6799F1065672 for ; Thu, 24 Nov 2011 19:29:43 +0000 (UTC) (envelope-from apseudoutopia@gmail.com) Received: from mail-bw0-f54.google.com (mail-bw0-f54.google.com [209.85.214.54]) by mx1.freebsd.org (Postfix) with ESMTP id EB4598FC08 for ; Thu, 24 Nov 2011 19:29:42 +0000 (UTC) Received: by bkbzs8 with SMTP id zs8so4313873bkb.13 for ; Thu, 24 Nov 2011 11:29:41 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; bh=zjYl1BT8ta9VVUKhospoZVsdVixucBRDifuQQuTd65c=; b=nqzClZq+cNrmf5vNgn6l3mBEP78sOctx/zaqCij/v8JAzUPDWRV0+LKQZk/NQkYDeZ T3YZ3EC0PWwVjWIeGJirGkin0Id4z6dqexZVldjXuL6hdEgOayk5PFLxkYQ9vzC8QJAq TtLY1tRHOQ5SfvA7tEg3KFCXBHZKI3YYHk41U= MIME-Version: 1.0 Received: by 10.205.135.129 with SMTP id ig1mr30790762bkc.106.1322162981541; Thu, 24 Nov 2011 11:29:41 -0800 (PST) Received: by 10.204.133.215 with HTTP; Thu, 24 Nov 2011 11:29:41 -0800 (PST) In-Reply-To: <4ECE9A7F.9000107@infracaninophile.co.uk> References: <88f3d8e819b3420f8e61723bee90ba5e.squirrel@www.magehandbook.com> <4ECB580E.20203@infracaninophile.co.uk> <4ECE9A7F.9000107@infracaninophile.co.uk> Date: Thu, 24 Nov 2011 14:29:41 -0500 Message-ID: From: APseudoUtopia To: Matthew Seaman Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Cc: freebsd-questions@freebsd.org Subject: Re: Setting up ZFS - Filesystem Properties and Installing on Root X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 24 Nov 2011 19:29:43 -0000 On Thu, Nov 24, 2011 at 2:26 PM, Matthew Seaman wrote: > On 24/11/2011 19:19, APseudoUtopia wrote: >> On Tue, Nov 22, 2011 at 3:06 AM, Matthew Seaman >> wrote: >>> On 22/11/2011 02:09, APseudoUtopia wrote: >>>> Another quick question about swap: If I have 4 drives, with 512MB >>>> swap, the system uses all 4 swap partitions, correct? So it's not like >>>> it'd be going to waste? I'd have a total of 2 GB swap? >>> >>> Well, yes. =C2=A0If you just declare those raw partitions to be swap ar= eas, >>> that will be the case. =C2=A0However, doing this is asking for trouble:= you >>> subvert any resilience features obtained by using ZFS with raidz1. =C2= =A0If >>> any one of the drives fails, your swap area will break and your system >>> will probably crash. >>> >>> Better to set up two pairs of gmirrors for swap -- the procedure is >>> described here: http://wiki.freebsd.org/RootOnZFS/GPTZFSBoot/Mirror >>> in section3 "Finish Install." =C2=A0This will effectively give you a ra= id10 >>> for your swap, with a total size of 1GB. >>> >> >> I'm not sure I understand this. How would that negatively affect the >> raidz1? The swap isn't in the zpool. I understand the system may crash >> if the OS was using the swap space and the drive failed. But would you >> not be able to reboot into a degraded zpool state and still have a >> usable system? >> > > No -- it means a failed disk can cause your system to crash. =C2=A0That's= not > resilient behaviour. =C2=A0Yes, the data on the ZFS raidz1 should survive= the > crash and the reboot, but the point is ZFS raidz1 should be able to > survive a disk failure like that /without/ a system crash. > Ah! I understand. Thank you for the explanation.