[Beowulf] Raid disk read performance issue in Linux 2.6, anyone seen this?

Craig Tierney ctierney at hpti.com
Tue Dec 7 14:25:44 EST 2004


On Mon, 2004-12-06 at 23:44, Chris Samuel wrote:
> On Sun, 5 Dec 2004 04:42 am, Craig Tierney wrote:
> 
> > For the 2.4 kernels, I needed to tweak /proc/sys/vm/max_readahead
> > to improve performance.
> 
> Out of interest, what was your tweak ?
> 
> cheers!
> Chris


The max_readahead is too small for high performance RAID
hardware.  I typically set:

echo 511 > /proc/sys/vm/max_readahead

But it depends.  If I am using LVM to stripe across volumes
I have seen better performance with 1023.  I would test
out different values, but I have never seen where the default
value of 31 was adequate.

I also changed /proc/sys/vm/min_readahead, but that didn't
seem to make a difference on the large streaming IO opterations.

Craig



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