Date: Sun, 15 Mar 1998 17:15:06 -0800 (PST) From: Simon Shapiro <shimon@simon-shapiro.org> To: Raul Zighelboim <rzig@gulfsouth.verio.net> Cc: "scsi@freebsd.org" <scsi@FreeBSD.ORG> Subject: RE: to raid or not to raid Message-ID: <XFMail.980315171506.shimon@simon-shapiro.org> In-Reply-To: <A03CD00C69B1D01195AB00A024ECEB167110DC@kaori.communique.net>
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On 16-Mar-98 Raul Zighelboim wrote: > > My missing link is: > > Will a (7 drive array under raid 5) be faster than a sinlg larger drive > ?... > Will it be as fast as a (5 drive raid 5 array) ? Depends a lot on who/what executes which RAID code. If you are running in-kernel RAID on a 486 which is overwhelmed with (let's say) network traffic, you may suffer greatly. If you use a deidicated RAID controller that does all the RAID-5 bit twidling in dedicated hardware and has 100IPS and 256MB of RAM to do it with, RAID-5 may appear faster than another solution's RAID-0. All else being equal, RAID-5, in optimal state, should be able to read almost as fast as RAID-0. Should be able to write about as fast as a single disk. increasing the number of stipes (drives) in a RAID-5 arrays slows WRITE operation worse than linear. READ improves more or less linearly. I have successfully run 10-12 drives in a RAID-5 arrangement on a DPT PM3334UDW, balanced on ONE bus. Throughput is about 8/4 MB/Sec READ/WRITE. On a dual bus arrangement, 14 drives went up to 15/7. Lots of caching. But this is not an inexpensive arrangement. Generally you can assume that, for a Unix filesystem traffic, you will saturate aSCSI bus with 4-8 drives. Simon To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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