Re: Dumb question: Which is "better" SCSI or IDE disks?

Christopher Smith (
Mon, 7 Dec 1998 02:27:16 -0500 (EST)

On Mon, 7 Dec 1998, Leonard Zhang System Administrator ISD RVIB wrote:
> Open server 5.0.4p, DPT RAID-1, 32 MB cache, PCI, 4.2 GB (A cable)
> copy 9,177 K in 9 seconds.
> Red hat 4.2, 8 GB IDE
> copy 9,397 K in 2 seconds.
> both run in shell script.
And the script was???

This is just a case of silly benchmarking. Do you really believe that IDE
is 4x faster than SCSI? All those big server vendors must be idiots eh?

Well, based on this, your IDE drive is so fast it ever outperforms RAM!
;-) (You are copying ~9 MB through a controller with 32 MB of cache.) My
suspicion is that your DPT RAID-1 controller with 32 MB cache is setup
with write caching disabled, as is the case for your SCSI hard disks. This
is one area where SCSI performance typically lags behind that of IDE,
because SCSI hard disk vendors typically setup their caches to not do
write caching by default (this can typically be changed, however). This is
because SCSI is typically used in servers, and many servers need to be
able to guaruntee at certain points that data has been comitted to hard
disk (databases typically have requirements like this).

Based on the information you've provided, it seems apparent that you are
testing with 2 different drives. Of course, you are also comparing two
entirely different OS's (ok, they're both Unixes, but SCO Open server is a
pig, and we all know it). On top of that you're dealing with two totally
different filesystems. I wonder if you are even using the same hardware
(CPU/memory/etc). What exactly do you think this benchmark proves?

Last but not least, Alan's point has been that for REAL WORLD tasks SCSI
performs a lot better because you are doing lots of random access on a
disk at the same time. For benchmark type operations IDE can outperform
SCSI, because the protocol is much simpler and therefore has lower
overhead. Alternatively, when you're in a real world where you have to do
multiple tasks at once, you'll find SCSI does a lot better than the
benchmarks indicate (more accurately, IDE does a lot worse).


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