From owner-freebsd-questions Mon May 7 17: 8:47 2001 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 A144937B422 for ; Mon, 7 May 2001 17:08:39 -0700 (PDT) (envelope-from grog@lemis.com) Received: by wantadilla.lemis.com (Postfix, from userid 1004) id 4FEBC6ACBE; Tue, 8 May 2001 09:38:37 +0930 (CST) Date: Tue, 8 May 2001 09:38:37 +0930 From: Greg Lehey To: Linh Pham Cc: Bob Greene , "Andrew C. Hornback" , Steve Blanzy , FreeBSD Questions Subject: Re: Raid Message-ID: <20010508093837.A66817@wantadilla.lemis.com> References: <3AF6CCDB.F1029665@tclme.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: ; from lplist@closedsrc.org on Mon, May 07, 2001 at 09:21:33AM -0700 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 Monday, 7 May 2001 at 9:21:33 -0700, Linh Pham wrote: > On 2001-05-07, Bob Greene scribbled: > >> Well, you wrote the book; I've only read it. Is this a vinum specific >> performance penalty? I suppose you're talking about the requirement to read before writing. No, that's not a Vinum-specific problem. All RAID-5 systems must do that. > I think the performance penalty affects almost every RAID 5 array, > since you have to update the ECC data on all of the remaining drives > so that the entire file system is still accessible. I didn't mention this "penalty", because it's insignificant. One of the reasons that Vinum performs better than many "hardware" arrays is because the processor on a PC is much faster. Even on the 486/66 on which I originally developed Vinum, the parity calculations were of hardly any relevance. > If I remember correctly... you can still have all your data as long > as no more than one drive were to fail in a single array at any > given time. To unmangle that... if you lost one drive already and > another one fails... I think your screwed. Correct. I mentioned that in my earlier message. There are significant performance penalties for recovering data from a degraded array. Write performance, on the other hand, is better when the array is degraded. Greg -- 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