Re: Two identical systems, radically different performance

On 9.10.2012 01:03, Craig James wrote:
>
>
> On Mon, Oct 8, 2012 at 3:50 PM, Claudio Freire <klaussfreire@gmail.com
> <mailto:klaussfreire@gmail.com>> wrote:
>
>     On Mon, Oct 8, 2012 at 7:48 PM, Craig James <cjames@emolecules.com
>     <mailto:cjames@emolecules.com>> wrote:
>     >> >  # blockdev --getra /dev/sdb1
>     >> > 256
>     >>
>     >>
>     >> It's probably this. 256 is way too low to saturate your I/O system.
>     >> Pump it up. I've found 8192 works nice for a system I have, 32000 I
>     >> guess could work too.
>     >
>     >
>     > But again ... the two systems are identical.  This can't explain it.
>
>     Is the read-ahead the same in both systems?
>
>
> Yes, as I said in the original reply (it got cut off from your reply):
> "Same on both servers."

And what about read-ahead settings on the controller? 3WARE used to have
a read-ahead settings on their own (usually there are three options -
read-ahead, no read-ahead and adaptive). Is this set to the same value
on both machines?

Tomas