Date: Wed, 14 Jun 2000 04:26:23 -0700 From: Greg Lehey <grog@lemis.com> To: Jaye Mathisen <mrcpu@internetcds.com> Cc: hackers@FreeBSD.ORG Subject: Re: Has anybody looked at RAID-5 vinum performance on the "whole system"? Message-ID: <20000614042623.N5769@sydney.worldwide.lemis.com> In-Reply-To: <Pine.BSF.4.21.0006131635260.11271-100000@schizo.cdsnet.net> References: <Pine.BSF.4.21.0006131635260.11271-100000@schizo.cdsnet.net>
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On Tuesday, 13 June 2000 at 16:39:01 -0700, Jaye Mathisen wrote: > > I was just curious what people's thoughts were on the potential "total > system throughput" (whatever you choose it to be), wrt using software > RAID. > > It would seem that software RAID would just kill big chunks of > cache, especially CPU cache, moving lots of data throught it to > calcuate CRC's. Hmm. Yes, it might seem that way, but that's a very different order of magnitude from the I/O transfers themselves. > perhaps the raid 1/0's would be fine, since the calcuation could be > ignored. Well, there is no calculation. > It would seem that for file-server type tasks, where hopefully CPU > is not an issue, then as long as you can exceed the capacity of your > network, you're probably fine. > > And most workstations probably don't run 100% (modulo things like > the various crackers and seti), that it's a non issue. It's a non-issue anyway. The RAID-5 parity calculations don't take up any time. The real issue is that each write requires two physical reads and two physical writes, reducing write performance to about 25% of the performance of RAID-1 writes. Take a look through http://www.lemis.com/vinum.html for further details. 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-hackers" in the body of the message
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