Date: Wed, 12 Jul 2000 11:31:50 +0930 From: Greg Lehey <grog@lemis.com> To: Rahul Siddharthan <rsidd@physics.iisc.ernet.in> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: Vinum/RAID-5 on IDE disks Message-ID: <20000712113150.E29642@wantadilla.lemis.com> In-Reply-To: <20000712004443.A6134@physics.iisc.ernet.in> References: <20000712004443.A6134@physics.iisc.ernet.in>
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On Wednesday, 12 July 2000 at 0:44:43 +0530, Rahul Siddharthan wrote: > On a system with 2 IDE buses and 4 disks (2 per bus), is it a good > idea to use RAID 5 / Vinum? No. > I read of issues regarding performance and fault tolerance on linux > raid when you put two disks on one bus, and it sounded like that > should apply to freebsd too, but I can't find a specific mention in > the vinum documentation. It's there somewhere. The problem is that striped organizations (including RAID-4 and RAID-5) write simultaneously to multiple drives, but an IDE controller can only handle one request at a time, so the second request has to wait until the first one is finished, effectively halving the performance. Write performance is pretty bad anyway with RAID-[45], so this is a serious drawback. > One problem mentioned there that if a disk goes down, it can take > the bus and therefore the other disk down with it: it doesn't matter > if the data on the other disk is safe and therefore the system can > be brought back up without data loss. But is there a likelihood of > the other disk being corrupted in such an event? There's always a possibility, and if the master drive goes down well enough, it will take the slave drive with it. > If there are performance issues with slave disks, are they likely to > be show-stopping? Any real-world experiences? It's not so much the slave by itself, it's the combination of master and slave which causes the problems. 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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