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Date:      Sun, 6 May 2001 10:16:18 +0930
From:      Greg Lehey <grog@lemis.com>
To:        "Andrew C. Hornback" <hornback@wireco.net>
Cc:        Steve Blanzy <sblanzy@aperion.com>, FreeBSD Questions <questions@FreeBSD.ORG>
Subject:   Re: Raid
Message-ID:  <20010506101618.B39554@wantadilla.lemis.com>
In-Reply-To: <000701c0d581$3dd2da60$0e00000a@tomcat>; from hornback@wireco.net on Sat, May 05, 2001 at 12:34:23PM -0400
References:  <000a01c0d57f$2158bb40$0400a8c0@192.168.0.1> <000701c0d581$3dd2da60$0e00000a@tomcat>

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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.

>> 	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.

>> 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.

You can set up RAID either with a specialized controller ("hardware
RAID") or with Vinum (see vinum(4) and vinum(8), also
http://www.vinum-vm.org/).

Greg
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