Re: Raid 10 chunksize

Scott Marlowe wrote:
> On Tue, Mar 24, 2009 at 7:09 PM, Mark Kirkwood <markir@paradise.net.nz> wrote:
>   
>> I'm trying to pin down some performance issues with a machine where I work,
>> we are seeing (read only) query response times blow out by an order of
>> magnitude or more at busy times. Initially we blamed autovacuum, but after a
>>  tweak of the cost_delay it is *not* the problem. Then I looked at
>> checkpoints... and altho there was some correlation with them and the query
>> response - I'm thinking that the raid chunksize may well be the issue.
>>     
>
> Sounds to me like you're mostly just running out of bandwidth on your
> RAID array.  Whether or not you can tune it to run faster is the real
> issue.  This problem becomes worse as you add clients and the RAID
> array starts to thrash.  Thrashing is likely to be worse with a small
> chunk size, so that's definitely worth a look at fixing.
>
>   

Yeah, I was wondering if we are maxing out the bandwidth...
>> Fortunately there is an identical DR box, so I could do a little testing.
>>     
>
> Can you try changing the chunksize on the test box you're testing on
> to see if that helps?
>
>   

Yes - or I am hoping to anyway (part of posting here was to collect some 
outside validation for the idea). Thanks for your input!


Cheers

Mark