atom feed6 messages in org.freebsd.freebsd-scsiRe: RAID performance/benchmarking
FromSent OnAttachments
Brandon HueyApr 14, 1998 12:41 pm 
Andreas KlemmApr 14, 1998 2:12 pm 
Simon ShapiroApr 14, 1998 4:52 pm 
Justin T. GibbsApr 14, 1998 5:54 pm 
TomApr 14, 1998 6:24 pm 
Simon ShapiroApr 14, 1998 9:18 pm 
Subject:Re: RAID performance/benchmarking
From:Simon Shapiro (shi@simon-shapiro.org)
Date:Apr 14, 1998 9:18:52 pm
List:org.freebsd.freebsd-scsi

On 15-Apr-98 Justin T. Gibbs wrote:

In article <XFMa@simon-shapiro.org> you wrote:

Depends on array size, type of controller, amount of cache, type of access. RAID arrays are not a good benefit for sequential access.

This really depends. For Pluto's application, using RAID 3 not only gives us reliability, but also the ability to have one of the drives in a stripe "return late", but still maintain low latency by replacing the data through parity reconstruction.

You are one of the few who still build RAID-3 arrays. Interesting... Since we are a realtime system where being even a

little late is unacceptable, the use of RAID gives us a big advantage. Almost all of our accesses are sequential.

I did not say that RAID arrays are not functionaly correct for Sequential access. Just that perfromance in RAID arrays is les than optimal when doing sequential access. In your case you ``do not have a choice'' but to use a RAID (3, 5 or otherwise), as you cannot afford data disruption. Simply, there is nothing free. If you want the reliability and availability that a redundant array provides, there will be a performance and capacity penalty.

BTW, the next generation DPT cards does all the parity computations in hardware. Makes some difference in WRITE perfrormance and in degraded READ.

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Sincerely Yours,

Simon Shapiro Shi@Simon-Shapiro.ORG Voice: 503.799.2313

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