[CentOS] Optimum Block Size to use

Wed Aug 19 15:56:56 UTC 2015
Jatin Davey <jashokda at cisco.com>

On 8/19/2015 4:17 PM, Leon Fauster wrote:
> Am 19.08.2015 um 10:24 schrieb John Hodrien <J.H.Hodrien at leeds.ac.uk>:
>> On Wed, 19 Aug 2015, Jatin Davey wrote:
>>
>>> Hi All
>>>
>>> We use CentOS 6.6 for our application. I have profiled the application and find that we have a heavy requirement in terms of Disk writes. On an average when our application operates at a certain load i can observe that the disk writes / second is around 2 Mbps (Average).
>> Initial thought is, do you really care?  2Mbps is peanuts, so personally I'd
>> leave everything at the defaults.  There's really no need to optimise
>> everything.
>>
>> Obviously the exact type of writes is important (lots of small writes written
>> and flushed vs fewer big unsynced writes), so you'd want to poke it with
>> iostat to see what kind of writes you're talking about.
>
>
> to address this we use (sysctl)
>
> vm.dirty_expire_centisecs
> vm.dirty_writeback_centisecs
>
> furthermore check the fs alignment with
> the underlying disk ...
>
> --
> LF
[Jatin]
These options deal with "caching" the writes. Correct me if i am wrong.
If it is indeed dealing with caching then i think it will not help 
because the application workload generates a lot of data that is always 
new. The application logic continously generates new data to be written 
to disk.
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Thanks
Jatin