Re: Help with low raid5 performance

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Mon, Jan 24, 2011 at 03:18:31PM +0000, Stephen Borrill wrote:
> 
> I've run the tests through and it doesn't help much. RAID5 on 3
> disks _is_ significantly quicker than on 4 (4x quicker for character
> writes and 7x for block writes). But contig 3 vs contig 4 and using
> -f 2048 -b 16384 make little difference (a handful of % at best).

It's possible you're being thwarted by the way UVM/UBC do "clustering";
I have a vague memory they ignore the maxcontig value and just cluster
to 64K.  I'd have to go digging in the code, though, and no time right
now...

Thor