From owner-freebsd-stable@FreeBSD.ORG Tue Sep 1 15:56:25 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 5E8EB1065696 for ; Tue, 1 Sep 2009 15:56:25 +0000 (UTC) (envelope-from petefrench@ticketswitch.com) Received: from constantine.ticketswitch.com (constantine.ticketswitch.com [IPv6:2002:57e0:1d4e:1::3]) by mx1.freebsd.org (Postfix) with ESMTP id 268228FC1F for ; Tue, 1 Sep 2009 15:56:25 +0000 (UTC) Received: from dilbert.rattatosk ([10.64.50.6] helo=dilbert.ticketswitch.com) by constantine.ticketswitch.com with esmtps (TLSv1:AES256-SHA:256) (Exim 4.69 (FreeBSD)) (envelope-from ) id 1MiViT-000KrK-7U; Tue, 01 Sep 2009 16:56:17 +0100 Received: from petefrench by dilbert.ticketswitch.com with local (Exim 4.69 (FreeBSD)) (envelope-from ) id 1MiViS-0004N3-U2; Tue, 01 Sep 2009 16:56:16 +0100 To: fjwcash@gmail.com, freebsd-stable@freebsd.org In-Reply-To: Message-Id: From: Pete French Date: Tue, 01 Sep 2009 16:56:16 +0100 Cc: Subject: Re: zfs on gmirror slice 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: Tue, 01 Sep 2009 15:56:25 -0000 > ZFS includes support for RAID0 (stripe), RAID1 (mirroring), RAID5 and RAID6 > (raidz1/raidz2), and (soon in OpenSolaris) RAID7 (raidz3). Why would you > want to build a pool out of devices that are already RAID'd together? Because gmirror type RAIDing is more appropriate for your application than ZFS RAID ? I am not the original poster, but I can easily see why one would want to do do this. For example making a gmirror of a local drive and a remote drive - you can ask gmirror to prefer reads on the local disc, but there isn't a way to specify that in ZFS that I know of. Also gmirror on top of ggate behaves nicely if the remote drive fails. ZFS does not behave nicely at all - or it didn't when I ran tests. I havent tried on the latest version I admit. But ZFS as a filesystem still has many significant advantages, so runnng it on top of gmirror is actually a worthwhile thing to do. -pete.