Slow PCI-X controller perfomance (adaptec 2130SLP)

Vasim Valejev vasim at
Fri Aug 26 12:23:18 GMT 2005

Hi !

> Whenever people complain about slow performance with AAC products and
> try to point the finger at the driver, I ask them do repeat their
> benchmark under linux and see how it compares.  Then they realize just
> how good they have it with FreeBSD.  I've worked very hard over the
> years to make the FreeBSD driver be the fastest driver available for
> AAC cards.

Yep, you was right, FreeBSD was a lot faster. The linux (Fedora Core, 2.6.11
kernel) got slightly better read speed but writes were 2-3 times slower (about
20-24 MB/s with 64k stripe). Not sure if i did everything correctly under linux
but that was really low.

> Your particular test is testing the following things:
> 1) disk transfer speed
> 2) controller firmware efficiency
> 3) cache memory bandwidth on the controller
> 4) stripe alignment of the requests
> 5) PCI-X bandwidth
> Your disk transfer speed is going to be about 70MB/s per disk.  Given
> that you are doing RAID-5 on 4 disks, you'll ideally get 3x70MB/s =
> 210MB/s.  The reason that you multiply by 3 and not 4 is that for a
> given stripe, you only have 3 disks that contain data, with the 4th
> disk containing parity information.  Also note that you are dealing
> with Ultra320.  Adding more disks than what you have will start to
> saturate the bandwidth of the bus (which is probabl between 260-300MB/s
> depending on a lot of factors)

I've made RAID-5 array (64k stripe) with all six disks but didn't got better
than 80..90 MB/s for 2GB file write (on /usr partition with bs=256k) and 133
MB/s  read from raw device (first 2GB of /dev/aacd0 with bs=256k, turning off
read caching doesn't make any difference). That isn't bad either, so i'll stay
with that. But it looks like some kind of bandwidth limit somewhere.

Vasim V.

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