Re: Two identical systems, radically different performance

On 09/10/12 11:48, Craig James wrote:
> On Mon, Oct 8, 2012 at 3:44 PM, Claudio Freire <klaussfreire@gmail.com>wrote:
>
>> On Mon, Oct 8, 2012 at 7:25 PM, Craig James <cjames@emolecules.com> wrote:
>>>>> But why? What have I overlooked?
>>>> Do you have readahead properly set up on the new one?
>>>
>>>   # 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.
>

Maybe check all sysctl's are the same - in particular:

vm.zone_reclaim_mode

has a tendency to set itself to 1 on newer hardware, which will reduce
performance of database style workloads.

Cheers

Mark