Date: Sat, 5 May 2001 22:57:11 -0400 From: "Andrew C. Hornback" <hornback@wireco.net> To: "Greg Lehey" <grog@lemis.com> Cc: "FreeBSD Questions" <questions@FreeBSD.ORG> Subject: RE: Raid Message-ID: <001f01c0d5d8$3ed3e420$0e00000a@tomcat> In-Reply-To: <20010506101618.B39554@wantadilla.lemis.com>
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> -----Original Message----- > From: owner-freebsd-questions@FreeBSD.ORG > [mailto:owner-freebsd-questions@FreeBSD.ORG]On Behalf Of Greg Lehey > Sent: Saturday, May 05, 2001 8:46 PM > To: Andrew C. Hornback > Cc: Steve Blanzy; FreeBSD Questions > Subject: Re: Raid > > [Format recovered--see http://www.lemis.com/email/email-format.html] > > Paragraphs have no line breaks. > > On Saturday, May 05, 2001 12:19 PM, Steve Blanzy wrote: > > On Saturday, 5 May 2001 at 12:34:23 -0400, Andrew C. Hornback wrote: > >> What RAID if any does free BSD support in a dual SCSI hard > drive configuration? > > > a> (ACK! Please don't send HTML-ized e-mail to the list!) > > In fact, his message was multipart-alternative. Your MUA shouldn't > have any difficulty with that. But please adjust it to make text > lines of < 80 characters. It should have been set to break lines at 76 characters... of course, it's a Microsoft client... *shakes his head* Guess I should apologize, eh? > >> And about your question... from personal experience, the only > >> two forms of RAID that you can use with two drives, no matter which > >> OS, are RAID 0 and RAID 1. > >> > >> RAID 0 is pure striping across both drives, which offers no > >> redundancy but may offer better throughput. > > In fact, as the number suggests, this isn't RAID (Redundant Array of > (Inexpensive) Disks) at all. Might be more aptly called AID, as there's no redundancy involved. > >> RAID 1 is pure mirroring, which offers the best redundancy but may > >> cause a severe penalty on disk subsystem performance. > > No, RAID-1 gives you the best performance of any RAID setup. The > reason why you need at least 3 disks for RAID-5 is because it is > slower, and though it would theoretically work with only two disks, > it has no advantages over RAID-1 in this configuration. I'm wondering about the explanation here, as I've always been told (and taught) that RAID 5 offers the best performance of any RAID level. This may be dependant on a few things (i.e. burst transfer rates of the drives and the controller), etc. RAID 1 causes a performance hit during write, as the data to be written has to be done twice. RAID 1 is really recommended when you absolutely must have the data available, because it allows for two copies to be stored. RAID 5, I would imagine, suffers a performance penalty in the whole comparison with the parity record, but, as I mentioned before, would perform better if the total burst transfer rate of the drives was equal to the burst transfer rate of the controller, if the controller's hardware handled the parity. (My knowledge of exactly how a RAID controller works is spotty, at best...) --- Andy To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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