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

[Roy Sigurd Karlsbakk]

> <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

--
Roy Sigurd Karlsbakk, MCSE, MCNE, CLS, LCA

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