[5374] in linux-scsi channel archive
Re: Dumb question: Which is "better" SCSI or IDE disks?
daemon@ATHENA.MIT.EDU (Gregory Maxwell)
Wed Dec 9 20:50:25 1998
Date: Wed, 9 Dec 1998 10:20:58 -0500 (EST)
From: Gregory Maxwell <linker@z.ml.org>
To: Christopher Smith <cbsmith@envise.com>
cc: Leonard Zhang System Administrator ISD RVIB <leonardz@rvib2.rvib.org.au>,
linux-kernel@vger.rutgers.edu, linux-scsi@vger.rutgers.edu
In-Reply-To: <Pine.LNX.4.04.9812080810490.7979-100000@localhost>
On Tue, 8 Dec 1998, Christopher Smith wrote:
> On Tue, 8 Dec 1998, Leonard Zhang System Administrator ISD RVIB wrote:
> > RAID-1 is disk mirror. DPT is cache with RAID. RAID will increase the
> > disk performance.
> Ugh.. FYI, RAID does not always increase disk performance, and in
> particular RAID-1 is guarunteed not to increase disk performance by it's
What? Join the real world but. Raid-1 doubles read throughput and the
slowdown of writes is negligable.
> very nature (ok, it's conceivable that read performance could be
> increased somewhat, but write performance would, if anything, be decreased
> somewhat). Again, if the cache is actually playing a role in this
> benchmark, then what you are really saying is that IDE is so fast that
> it's 4x faster than DPT's cache memory. Think about that for a minute.
Come off it, when you do disk benchmarks you use a dataset sufficently
large so that the cache doesn't matter. Linux does caching just fine,
DPT's cache is somewhat redundant.
Almost all other raid levels perform worse (like raid 5 where the fastest
write takes 2 reads 1 block XOR and 1 write).
The fastest raid array is a combo of raid-0(striping) and raid-1.
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