Date: Mon, 9 Nov 1998 17:14:58 +1030 From: Greg Lehey <grog@lemis.com> To: "Justin T. Gibbs" <gibbs@plutotech.com> Cc: "Kenneth D. Merry" <ken@plutotech.com>, bill@bilver.magicnet.net, freebsd-fs@FreeBSD.ORG Subject: Re: RAID-3 and RAID-4 (was: RAID1 Software vs Hardware) Message-ID: <19981109171458.A15539@freebie.lemis.com> In-Reply-To: <199811090629.XAA25531@pluto.plutotech.com>; from Justin T. Gibbs on Sun, Nov 08, 1998 at 11:23:04PM -0700 References: <19981109165612.K499@freebie.lemis.com> <199811090629.XAA25531@pluto.plutotech.com>
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On Sunday, 8 November 1998 at 23:23:04 -0700, Justin T. Gibbs wrote: >>> RAID-3 confines parity to 1 member of the array. The size of the stripe >>> is not a part of the specification. In the case of Pluto products, we >>> usually use a stripe size of 1MB which implies a per-unit access of >>> 1MB/N-1 (N being number of members in the RAID group). >> >> This looks like RAID-4 to me. Where do you see the difference? > > RAID-4 adds the ability to do smaller than whole stripe updates with only > touching the affected members of the stripe and the parity. RAID-3 > concerns itself only with whole strip accesses. Since we have full control > over the stripe size and know in advance the type of data we will store > and the way it is accessed, RAID-3 is sufficient for Pluto's application. Hmmm. I looked up my references and found that they are obviously incorrect, though I hadn't noticed that before. Where (on the web) can I find a reliable definition? If I see this correctly, then, are you saying the big difference between RAID-3 and RAID-4 is in the software, not in the storage layout? Greg -- 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-fs" in the body of the message
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