From owner-freebsd-questions Tue Jul 11 19: 2:21 2000 Delivered-To: freebsd-questions@freebsd.org Received: from wantadilla.lemis.com (wantadilla.lemis.com [192.109.197.80]) by hub.freebsd.org (Postfix) with ESMTP id 6B0F037BB13 for ; Tue, 11 Jul 2000 19:02:12 -0700 (PDT) (envelope-from grog@wantadilla.lemis.com) Received: (from grog@localhost) by wantadilla.lemis.com (8.9.3/8.9.3) id LAA29904; Wed, 12 Jul 2000 11:31:50 +0930 (CST) (envelope-from grog) Date: Wed, 12 Jul 2000 11:31:50 +0930 From: Greg Lehey To: Rahul Siddharthan Cc: freebsd-questions@FreeBSD.ORG Subject: Re: Vinum/RAID-5 on IDE disks Message-ID: <20000712113150.E29642@wantadilla.lemis.com> References: <20000712004443.A6134@physics.iisc.ernet.in> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 1.0pre2i In-Reply-To: <20000712004443.A6134@physics.iisc.ernet.in> Organization: LEMIS, PO Box 460, Echunga SA 5153, Australia Phone: +61-8-8388-8286 Fax: +61-8-8388-8725 Mobile: +61-418-838-708 WWW-Home-Page: http://www.lemis.com/~grog X-PGP-Fingerprint: 6B 7B C3 8C 61 CD 54 AF 13 24 52 F8 6D A4 95 EF Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG 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