Re: software raid issues -- possible kernel I/O problem?

From: Roy Sigurd Karlsbakk (
Date: Sun Dec 09 2001 - 14:32:57 EST

> <snip />
> So, my observations are as follows:
> 1) It seems as though I can't get aggregate burst speeds up above about
> 100MB/s no matter what I do, even when it's on separate interfaces with
> separate IRQs. Is this running into the limitation of the PCI bus? I'm
> also somewhat confused as to how my old ata33 drive managed to score
> nearly 100MB/s burst speed, as well as how some people are claiming
> scores of 160MB/s on a ata100 drive (and why I'm not getting that on
> mine).

The 100MB/s is probably the PCI bus, yes. The theoretical limit of a
32bit,33MHz PCI bus is 33^6*32/8 = 132.000.000 = ~ 125MB/s. In practice,
there's always some overhead.

An ATA33 drive can't go over 33MB/s, as the bus don't deliver any more.
an ATA100 bus can give you 100MB/s, but there is currently no drive
available that can give you that. The fastest drive I've read about, is
the Western Digital WD1200BB (120 gig). They brag about pushing 525Mbit/s
from buffer to disk. That's some 65 megs per sec, which is pretty amazing.


Roy Sigurd Karlsbakk, MCSE, MCNE, CLS, LCA

Computers are like air conditioners. They stop working when you open Windows.

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