Date: Sun, 19 Sep 1999 11:50:52 +0930 From: Greg Lehey <grog@lemis.com> To: The Hermit Hacker <scrappy@hub.org> Cc: freebsd-questions@freebsd.org Subject: Re: mirroring one drive to another...vinum? Message-ID: <19990919115052.Z55065@freebie.lemis.com> In-Reply-To: <Pine.BSF.4.10.9909182247240.27097-100000@thelab.hub.org>; from The Hermit Hacker on Sat, Sep 18, 1999 at 10:57:12PM -0300 References: <19990919110524.U55065@freebie.lemis.com> <Pine.BSF.4.10.9909182247240.27097-100000@thelab.hub.org>
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On Saturday, 18 September 1999 at 22:57:12 -0300, The Hermit Hacker wrote: > On Sun, 19 Sep 1999, Greg Lehey wrote: > >>> what I want to do is mirror da0s1a->da1s1a, da0s1?->da0s1?, >>> etc...which, to my understanding, isn't even RAID-5, but RAID-1... >> >> Precisely. What kind of plex do you want in the mirror? Normally you >> wouldn't use RAID-5. > > You lose me here...if I try to equate this to what I know, is a 'plex' the > sam as what Solaris/Disksuite calls a 'metadevice'? I don't know. Judging by the name alone, it's possible, but there are other intermediate building blocks, such as the ones IBM uses. I describe what a plex is in the web page you've read. > Basically, under solaris/Disksuite, if I mirror /dev/dsk/c0t1d0s1 with > /dev/dsk/c1t1d0s1, I get /dev/md/dsk/d0...and its /dev/md/dsk/d0 that I > mount. If you mirror two (or more) plexes, you get a volume, and that's what you mount. > Under vinum, if I mirror /dev/da0s1a to /dev/da1s1a, I would get a 'plex'? You can't mirror two drives. You need to create subdisks. It's all described in the web page. >>> Basically, I want to mirror my system disk to a second drive on >>> the same size/make, so that if one dies, my whole system doesn't go >>> poof... >> >> Sounds like you need concatenated plexes. > > Huh? Again, its your terminology that is probably what is throwing me, > but if I concatenate /dev/da0s1a to /dev/da1s1a, the end result is the sum > of the two drives, where /dev/da0s1a would fill up first, then da1s1a ... > concatenating is what I'd use with hard drives of a different size to > combine them (ie. ccd). If I stripe, then I do the same, but both drives > have to be the same size (or, rather, both partitions have to be) and I > get a performance increase since it writes alittle to each drive to > spread the load... It looks like you need to read the web page. That's what it's there for. I can repeat it here, but that won't help much. > Again, my knowledge is based on how Disksuite talks about things.. > >> Then gain, I just checked 'man 4 vinum', and it also states it >> requires a minimum of 3... >> >> I don't see anything like that in vinum(4). > > o RAID-5 plexes require at least three equal-sized subdisks. Ah, OK. Note the beginning of the sentence. It makes *no* *sense* to have a RAID-5 plex with less than three subdisks. This has nothing to do with Vinum. >>> Please note that my use of RAID=1 is from the Solaris/DiskSuite >>> environment...I'm new to it with FreeBSD/Vinum :( >> >> You've been talking about RAID-5, which is not the same as RAID-1. To >> quote the web page, which is correct: >> >> Vinum imposes an additional, trivial restriction: a striped plex >> must have at least two subdisks, since otherwise it is >> indistinguishable from a concatenated plex. >> >> Vinum enforces a minimum of three subdisks for a RAID-5 plex, >> since any smaller number would not make any sense. >> >> There is no such restriction for concatenated plexes. > > Okay, we've got to be talking the same thing in two different languges :( > > How does this work? If I'm understanding you correctly...if I want to do > this, I have to "convert" /dev/da0s1a and /dev/da1s1a to "concatenated > plexes" consisting of one subdisk each, and then I RAID-1 the two plexes > together? It's all in the web page. If there's something there you don't understand, please tell me about it. > Or, in Disksuite-speak...convert the two subdisks to a metadevice > considering of one device and then link'ng the two together as RAID-1... This is getting closer. But you don't need more than one subdisk in a concatenated plex. > If this is correct...is there instructions/examples on how to do thsi with > the system disk? ie. /? Not possible yet. Greg -- When replying to this message, please copy the original recipients. For more information, see http://www.lemis.com/questions.html 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-questions" in the body of the message
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