Date: Fri, 31 Mar 2000 13:04:55 +1000 From: Greg Lehey <grog@lemis.com> To: "Niels Chr. Bank-Pedersen" <ncbp@bank-pedersen.dk> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: Can one do a striped volume with mirrored plexes Message-ID: <20000331130455.F6764@mojave.worldwide.lemis.com> In-Reply-To: <20000331045100.A50664@bank-pedersen.dk>; from ncbp@bank-pedersen.dk on Fri, Mar 31, 2000 at 04:51:01AM %2B0200 References: <20000330165535.C48576@bank-pedersen.dk> <20000331111613.A6178@mojave.worldwide.lemis.com> <20000331045100.A50664@bank-pedersen.dk>
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On Friday, 31 March 2000 at 4:51:01 +0200, Niels Chr. Bank-Pedersen wrote: > On Fri, Mar 31, 2000 at 11:16:13AM +1000, Greg Lehey wrote: >> On Thursday, 30 March 2000 at 16:55:35 +0200, Niels Chr. Bank-Pedersen wrote: >>> Hi, >>> >>> I have 3 Kingston DS-500 chassis' connected to 3 Tekram controllers, >>> and I want to create one volume/filesystem that must be resilient to > ^^^ >>> disk failure, chassis failure and controller failure. >>> >>> In vinum(8) it says that I can create a mirrored volume with two >>> striped plexes, but that would only give me resilience against disk >>> failure, so what I was thinking of was something like this: >>> >>> Chassis disks controller >>> >>> A 0 1 3 4 6 7 9 a x I >>> B 0 2 3 5 6 8 9 b x II >>> C 1 2 4 5 7 8 a b x III >>> >>> - where each number, 0-b (x being spare disks), represents a small >>> mirror of 2 disks, and then all mirrors should be striped together >>> to form one volume. >>> >>> With the above setup I believe I will have resilience >>> against all "single-unit failures" - be it disk, chassis or >>> controller, but I dont see any way to configure this with >>> vinum. >> >> Hmm. If I understand what you want here, this would do it: >> >> drive 0A device /dev/chassisA/drive0 >> <snip> >> volume 0 >> plex org striped 512k >> sd len 0b drive 0A >> sd len 0b drive 0B >> volume 1 >> plex org striped 512k >> sd len 0b drive 0C >> sd len 0b drive 1A >> >> (etc). > > I'm not sure I get this (or else I wasn't being clear about what > I want in the first place): Wouldn't this give me 12 seperate > volumes => 12 mountpoints (with the last 3 drives excluded)? Yes. > - And if I ommit all but the first volume statement like: > > volume 0 > plex org striped 512k > sd len 0b drive 0A > sd len 0b drive 0B > plex org striped 512k > sd len 0b drive 0C > sd len 0b drive 1A > (etc). > > then it is my understanding that I would get one volume mirrored > on 12 plexes (8, I believe, is the maximum number allowed). Correct, but you don't want more than 2 plexes. > Hmm, probably me missing something obvious here. Or I am. I understood that you wanted 12 separate volumes. Ah, yes, you did. But you also want a single volume, and you want to make it out of volumes you first thought of. Why do you want to want to do that? The only real issue you have here is that you need to ensure that the failure of any one component doesn't cause an overlapping hole in both plexes. You should be able to do this by taking the first chassis and the first half of the second chassis for the first plex, and the second half of the second chassis and the third chassis for the second plex. Then you have: - failure of first controller or chassis: the first plex loses the first two thirds of the address space. The second plex covers the entire address space, so there's no failure. - failure of third controller or chassis: the second plex loses the last two thirds of the address space. The first plex covers the entire address space, so there's no failure. - failure of the second controller: first plex loses last third of the address space. The second plex losts the first third of the address space. We still have complete coverage, since the losses don't overlap. 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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