From owner-freebsd-questions@FreeBSD.ORG Wed Oct 1 10:03:44 2008 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 2EE1C10656ED for ; Wed, 1 Oct 2008 10:03:44 +0000 (UTC) (envelope-from jdc@koitsu.dyndns.org) Received: from QMTA02.westchester.pa.mail.comcast.net (qmta02.westchester.pa.mail.comcast.net [76.96.62.24]) by mx1.freebsd.org (Postfix) with ESMTP id CA9A38FC13 for ; Wed, 1 Oct 2008 10:03:43 +0000 (UTC) (envelope-from jdc@koitsu.dyndns.org) Received: from OMTA11.westchester.pa.mail.comcast.net ([76.96.62.36]) by QMTA02.westchester.pa.mail.comcast.net with comcast id MMs11a00A0mv7h052N3LME; Wed, 01 Oct 2008 10:03:20 +0000 Received: from koitsu.dyndns.org ([67.180.253.227]) by OMTA11.westchester.pa.mail.comcast.net with comcast id MN3Q1a0034v8bD73XN3R6T; Wed, 01 Oct 2008 10:03:25 +0000 X-Authority-Analysis: v=1.0 c=1 a=QycZ5dHgAAAA:8 a=sVWJYEl37suGWVR63ewA:9 a=bDv6YNZKTyVTkHXdRrjvIl0hzGEA:4 a=EoioJ0NPDVgA:10 a=LY0hPdMaydYA:10 Received: by icarus.home.lan (Postfix, from userid 1000) id AC5D7C9432; Wed, 1 Oct 2008 03:03:41 -0700 (PDT) Date: Wed, 1 Oct 2008 03:03:41 -0700 From: Jeremy Chadwick To: Wojciech Puchar Message-ID: <20081001100341.GA16582@icarus.home.lan> References: <340a29540809302134p2414e3cfw6a0694026e57d879@mail.gmail.com> <20081001071150.GA13554@icarus.home.lan> <20081001092139.D7677@wojtek.tensor.gdynia.pl> <20081001090414.GA15939@icarus.home.lan> <20081001111736.O8258@wojtek.tensor.gdynia.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081001111736.O8258@wojtek.tensor.gdynia.pl> User-Agent: Mutt/1.5.18 (2008-05-17) Cc: "freebsd-questions@freebsd.org" , Andrew Falanga Subject: Re: Setting up gmirror 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: Wed, 01 Oct 2008 10:03:44 -0000 On Wed, Oct 01, 2008 at 11:19:01AM +0200, Wojciech Puchar wrote: >> And what exactly do you classify controllers such as the Promise TX4310 >> and the Promise S150 SX4 as? The TX4310 could be classified as >> "software RAID", but a few of the features are offloaded onto the >> controller. The SX4 is the same way, but has actual on-board cache. > > si it do something by hardware. anyway - i don't think it will actually > make it faster under FreeBSD (contrary to windoze). > > it's simply not worth money. > >> You like to declare everything as "software RAIDs", while I like to >> discern the difference between them using (what I believe to be) more >> accurate terminology: >> >> BIOS-level RAID (Adaptec HostRAID, Intel MatrixRAID; "chipset" RAID) >> OS-based RAID (gvinum, ccd, etc.) > > what are the difference between 1 and 2? > > there are none. With regards to Intel MatrixRAID, you're correct -- all the feature does is provide disk pairing features via the southbridge, and provide an option ROM which configures and manages metadata on the disks for the OS to read and make use of. All the I/O operations still have to go through the CPU, and nothing is off-loaded. The reason I discern the difference is because if you tell a user "yes, your Intel MatrixRAID is software RAID", they become confused, since the feature is provided on a dedicated chip (ICHx). "But software RAID is done in the operating system, like gvinum!" There is also one difference which you're forgetting: booting. FreeBSD has a long-standing history of not being able to boot off of most anything other than UFS and gmirror; I believe gvinum might work, but I've only been able to find confirmation that gmirror does. I'm under the impression gstripe doesn't, and ZFS definitely does not. By using an additional (lower) layer that the OS has no control over (e.g. MatrixRAID), you can get around this limitation, because the OS considers the disks a single device (e.g. /dev/ar0). Of course, you run into other problems using MatrixRAID on FreeBSD, specifically when a disk fails (see my Wiki page), and the negatives there easily outweigh the positives. If you have a RAID-0 configuration you want to boot from, I've no idea what will work. If you have a RAID-1 configuration you want to boot from, gmirror is a good choice. If you have a RAID-5 or other configuration you want to boot from, a software or hardware RAID controller would be sufficient (see above). -- | Jeremy Chadwick jdc at parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, USA | | Making life hard for others since 1977. PGP: 4BD6C0CB |