Date: Sat, 14 Jul 2001 09:28:21 +0930 From: Greg Lehey <grog@FreeBSD.org> To: Mark Drayton <mark.drayton@izr.com> Cc: freebsd-questions@freebsd.org Subject: Re: Vinum mirrored/striped confusion Message-ID: <20010714092821.F99931@wantadilla.lemis.com> In-Reply-To: <20010714004038.A58799@drex.staff.izr.com>; from mark.drayton@izr.com on Sat, Jul 14, 2001 at 12:40:39AM %2B0100 References: <20010714004038.A58799@drex.staff.izr.com>
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On Saturday, 14 July 2001 at 0:40:39 +0100, Mark Drayton wrote: > Hi > > I'm trying to set up a machine with a striped and mirrored set for use > with postfix and cyrus. From vinum(8): > > You may want to have the best of both worlds and have both resilience > and performance. This is sometimes called RAID-10 (a combination of > RAID-1 and RAID-0), though again this name is misleading. With vinum > you can do this with the following configuration file: > > drive d1 device /dev/da2e > drive d2 device /dev/da3e > drive d3 device /dev/da4e > drive d4 device /dev/da5e > volume raid setupstate > plex org striped 512k > sd length 512m drive d1 > sd length 512m drive d2 > sd length 512m drive d3 > sd length 512m drive d4 > plex org striped 512k > sd length 512m drive d4 > sd length 512m drive d3 > sd length 512m drive d2 > sd length 512m drive d1 > > I don't quite understand why mirroring two plexes containing the same > subdisks is beneficial. What happens if, say, disk 1 fails? If you mean d1, then you'll lose the first 512 MB of plex 0 and the last 512 MB of plex 1. These parts of the volume will no longer be mirrored. > I imagine both plexes will be faulty and the volume will be down This is incorrect. The volume will remain up. > which (to me) almost defies the point of mirroring. > > drive d1 device /dev/da2e > drive d2 device /dev/da3e > drive d3 device /dev/da4e > drive d4 device /dev/da5e > volume raid setupstate > plex org striped 512k > sd length 512m drive d1 > sd length 512m drive d2 > plex org striped 512k > sd length 512m drive d3 > sd length 512m drive d4 > > If disk 1 failed with this setup, will the volume still be up with one > of its plexes in the faulty state? Yes, the volume will still be up. > Aside from this possible difference, is one of these two setups > going to perform better (for a mail server) than the other? Well, the second config only has half the storage :-) But if you made those 1 GB subdisks, the performance should be comparable. Note that 512 kB stripes are suboptimal. I've fixed the man page in many places, but I see I've left some behind. Choose a stripe size in that order of magnitude which is not a power of 2. Greg -- When replying to this message, please copy the original recipients. If you don't, I may ignore the reply. For more information, see http://www.lemis.com/questions.html 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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