Date: Wed, 4 Nov 1998 15:09:46 +1030 From: Greg Lehey <grog@lemis.com> To: Steve Ames <steve@ns1.cioe.com>, steve@inc.net Cc: freebsd-isp@FreeBSD.ORG Subject: Vinum on root partition (was: disk mirroring?) Message-ID: <19981104150946.L784@freebie.lemis.com> In-Reply-To: <199811032205.RAA17243@ns1.cioe.com>; from Steve Ames on Tue, Nov 03, 1998 at 05:05:03PM -0500 References: <363F7C79.AEA2279C@inc.net> <199811032205.RAA17243@ns1.cioe.com>
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On Tuesday, 3 November 1998 at 17:05:03 -0500, Steve Ames wrote: >>> Can anyone recommend a non-hardware method of disk mirroring? What >>> I'm looking for is something akin to disk mirroring under NT4. ie >>> I add another drive, declare it and an old disk part of a mirror >>> set and data gets replicated and then subsequent writes go to both >>> drives. >> >> man ccd >> >> Should do what you need... > > Nope. ccd suffers from the same problems (for this application) as > vinum: > > - requires that you start with either 'ccd' devices or 'vinum' volumes > (existing data partitions need to be copied off and then back on...) Well, that depends, but in principle yes. > - no real support for mirroring the 'root' partition It's on its way. There's not much to do, but it needs to be done. > What I really need is an abstraction layer above the standard disk > devices where I can group a couple of standard disk partitiions > together and achieve simultaneous writes (ie I write to the abstract > layer, it writes to both partitions)... ccd and vinum both seem to > do this but what I don't see is the ability to stop using vinum and > just use the single partition if something happens to the other > drive. Ah, you're thinking in terms of ccd, where everything crashes if one drive goes down (thus lowering uptime instead of increasing it). If you lose one plex with Vinum, the others are unaffected. Here's a case from my test machine: vinum -> l -r obj V obj State: up Plexes: 2 Size: 400 MB P obj.p0 C State: up Subdisks: 2 Size: 400 MB P obj.p1 S State: down Subdisks: 4 Size: 400 MB S obj.p0.s0 State: up PO: 0 B Size: 200 MB S obj.p0.s1 State: up PO: 200 MB Size: 200 MB S obj.p1.s0 State: up PO: 0 B Size: 100 MB S obj.p1.s1 State: up PO: 100 MB Size: 100 MB S obj.p1.s2 State: up PO: 200 MB Size: 100 MB S obj.p1.s3 State: up PO: 300 MB Size: 100 MB > Also I can't seem to stripe. Everything comes out concatentated :) Both vinum and ccd can do both. You'll notice the "C" and "S" in the plex lines above, indicating one is concatenated, the other striped. > Then there the issue of no 'root' partition support. You said. Would you be interested if I implemented partition encapsulation? Basically, that would be a subdisk which is not part of a Vinum drive, so you could point to an existing disk partition. This would enable you to mirror in the way you planned, and would also make it easier to support root partitions. Greg -- See complete headers for address, home page and phone numbers finger grog@lemis.com for PGP public key To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-isp" in the body of the message
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