From owner-freebsd-current Mon Jan 6 15: 2:35 2003 Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 144EE37B401 for ; Mon, 6 Jan 2003 15:02:32 -0800 (PST) Received: from mail.allcaps.org (allcaps.org [216.240.173.16]) by mx1.FreeBSD.org (Postfix) with ESMTP id 9DC5E43EC2 for ; Mon, 6 Jan 2003 15:02:31 -0800 (PST) (envelope-from bsder@allcaps.org) Received: from mail.allcaps.org (localhost [127.0.0.1]) by mail.allcaps.org (Postfix) with ESMTP id 4B22492FA9; Mon, 6 Jan 2003 18:02:27 -0500 (EST) Received: from localhost (bsder@localhost) by mail.allcaps.org (8.12.5/8.12.5/Submit) with ESMTP id h06N2OKG016768; Mon, 6 Jan 2003 15:02:26 -0800 X-Authentication-Warning: mail.allcaps.org: bsder owned process doing -bs Date: Mon, 6 Jan 2003 15:02:24 -0800 (PST) From: "Andrew P. Lentvorski, Jr." To: Nate Lawson Cc: current@freebsd.org Subject: Re: mirrored root fs? In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On Mon, 6 Jan 2003, Nate Lawson wrote: > I'd like to have a mirrored root partition. I tried ccd(4) but the boot > blocks couldn't find the fs. Any idea how much work it would take to > enable booting a ccd root? Also, does vinum already support this? I gave this the old college try a while ago, here's what I found out about the different methods: 1) CCD -- no info I never really tried CCD as there seem to be much better options with atacontrol, vinum, and RAIDFrame. 2) 3Ware Escalade Cards Advantanges: They work like a charm and look just like a SCSI controller Disadvantages: Extra hardware. Expense. Proprietary. 3) atacontrol Probably your best choice right now if you have a real RAID controller on your motherboard. The BIOS takes care of most of the nasty booting details. If you don't have a real RAID controller on the motherboard, stop now. Rebuilds don't work if you don't have a real RAID controller. You can recover, but it requires some dancing with dd (search the archives). Advantages: BIOS handles bootup issues. Very little required from OS Disadvantages: Hardware required. Proprietary. Will not rebuild a broken array without hardware RAID The next two methods require only FreeBSD. They both share the same problem: you have to boot a kernel from somewhere non-RAID and then the kernel can "autodetect" RAID configurations as it boots. Autodetection of the RAID systems before mounting root is the key here. If something needs to mount / before it can configure, you can't mirror / since FreeBSD has no method for remounting /. Perhaps this has changed with the new GEOM code, somebody might want to ask Poul about this. 4) vinum ( http://www.vinumvm.org/ ) The older of the two general RAID systems for FreeBSD. vinum *can* be fairly complex as it was meant for doing more than just RAID (it is meant to be something akin to Veritas for full logical volume management). However, standard RAID 1 is a fairly simple configuration. At one point, I somehow managed to get vinum to autodetect /, but that was more than a year ago on -stable, I haven't tried -current. Advantages: No extra hardware required (beyond the disks themseleves). All code contained in FreeBSD (nothing proprietary) Does more than just RAID Disadvantages: Kernel required to be booted from somewhere non-RAID Unknown status with respect to SMP and GEOM 5) RAIDFrame ( http://people.freebsd.org/~scottl/rf/ ) RAIDFrame is the newer kid on the block in FreeBSD RAID. It is a port of the RAIDFrame code from NetBSD (which is itself a port of the RAIDFrame code from CMU, IIRC). Back in -stable within the last year, I managed to get RAIDFrame to autodetect on boot. Unknown in -current. Advantages: No extra hardware required (beyond the disks themseleves). All code contained in FreeBSD (nothing proprietary) Disadvantages: Kernel required to be booted from somewhere non-RAID Unknown status with respect to SMP and GEOM (although this stuff is on the radar screen) The following is not a true RAID solution, but it seems to be popular: 6) root partition pseudo-mirror using dd with RAID on other partitions ( http://ezine.daemonnews.org/200111/vinum.html ) This is what most people who use FreeBSD kernel-based RAID mirroring currently do. CAUTION: This does *not* have the reliability advantages of true RAID 1 mirroring. If the disk containing your root filesystem goes down, so does your system. This may not matter to you, but it is something you should be aware of. Advantages: No extra hardware required (beyond the disks themseleves). All code contained in FreeBSD (nothing proprietary) Kernel booted from pseudo-mirror Disadvantages: Root partition disk crash takes out system Manual copying of root partition required Mirroring with dd may fail on open files As always, these opinions are my own. Your mileage may vary. All disclaimers apply. Yadda, yadda, yadda, etc., etc. ;) Hope this helps, -a To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message