Date: Sat, 18 Dec 1999 09:00:44 +1030 From: Greg Lehey <grog@lemis.com> To: Morten Seeberg <morten@seeberg.dk> Cc: questions@FreeBSD.ORG Subject: Re: Mirroring boot-disk?? Message-ID: <19991218090044.B475@freebie.lemis.com> In-Reply-To: <06f301bf489e$c832d370$de00000a@SOS> References: <06f301bf489e$c832d370$de00000a@SOS>
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On Friday, 17 December 1999 at 15:55:33 +0100, Morten Seeberg wrote: > Hi, Im supposed to be in charge of a large FreeBSD installation this > weekend, and our plan was to mirror the bootdisk on all our servers, but the > guy whom I put in charge of finding how to do it, didn´t really do his > homework, so now Im asking: > > I´ve just searched through 8 months of questions@freebsd.org letters, and > i´m not sure about the capabilities of VINUM and CCD. Actually I´m a bit > confused to say the least :) > > Is it at all possible to mirror the bootdisk, so that if a disk fails during > production time, nothing happens? No. > Can I boot on the secondary disk afterwards, if the primary fails? > > If I can, could you give me a hint to what Im supposed to be looking > at? CCD, VINUM, other, and if you have tried it, some pointers to > save me some time. I'm surprised you haven't read http://www.lemis.com/vinum/wishlist.html: There are a number of features that I have been asked for in Vinum. This page summarizes them and their status. Vinum root file system It's currently not possible to mount the root file system on a Vinum volume. This is a chicken and egg problem: You can't start Vinum until the kernel is running, and the kernel needs to be mounted somewhere. There are at least four different possible ways to implement this: 1. Teach the bootstrap code about Vinum so that it could start Vinum and load directly from a Vinum volume. This is unlikely to be viable, since Vinum needs to know too much about the kernel environment. 2. Create a separate boot file system and put the kernel in there, then start Vinum and the root file system. This is the System V way, but I don't like it too much. 3. Create an MFS root file system. This effectively lives in swap, but there's no problem there. We'd need an easier way to build MFS kernels. 4. Boot normally, start Vinum and then mount the root file system on top of the old root file system. This might work, up to a point: you can mount a file system on any mount point, even if files are open in the hierarchy below the mount point. Unfortunately, there are a number of problems with this approach. In particular, you can't close all files on the old root partition, which means that you're not completely resilient. In addition, if you boot from the Vinum partition as a normal disk partition (which is possible and seems to make sense), you'll have consistency problems if you change a file on one partition and not the other, since the system sees the two partitions as separate. One possibility here would be for the mount operation to go through the vnodes for each open file and change them to point to the Vinum volume. It's likely that this will be a difficult operation to perform. Status: I'm still thinking about this one. It's the single most asked-for feature, and I'm very open to suggestions about how to implement it. > If it is not possible, then how would you do it? Some of you without > RAID controllers must have some way of keeping your bootdisk/system > safe? Pointers please? (Do you just backup your bootdisk every 15 > minutes or the like?) In fact, there isn't too much on the root file system which is needed for continued operation. You can move most of that to a different file system, leaving you just with the kernel on the root file system. But there's no really tidy way to do it. Greg -- When replying to this message, please copy the original recipients. For more information, see http://www.lemis.com/questions.html Finger grog@lemis.com for PGP public key See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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