Re: Reason for md raid1 max_sectors_kb limited to 127?

[Bernd Schubert <bernd.schubert@fastmail.fm>]

On 05/07/2012 05:33 PM, Sebastian Riemer wrote:
> On 07/05/12 16:47, Bernd Schubert wrote:
>> On 05/07/2012 04:44 PM, Roberto Spadim wrote:
>>> could check if it have any performace increase? maybe i consider
>>> upgrading my kernel to get more performace inn raid1
>>>
>>
>> Depends on your hardware. Hardware that can handle small IO sizes, such
>> as common hard disks usually don't have problems with 512KB IOs. But if
>> you should use software on top of hardware raid large IOs might be very
>> important (again depends on the hw-raid vendor then).
>>
>>
>> Cheers,
>> Bernd
>
> O.K., I've also tested 3.2.16 and there the problem still exists.
> Bernd pinpointed me to commit b1bd055d397e09f99dcef9b138ed104ff1812fcb
> (block: Introduce blk_set_stacking_limits function).
>
> After cherry-picking it on 3.2.16 it worked. Tomorrow I'll test the
> performance impact and verify it by block tracing.

You might want to check IO sizes with my a patched blkiomon (blktrace). 
I added a mode to make the IO table more verbose about actual io sizes. 
I always wanted to further improve it and to send patches upstream, but 
so far didn't find time for that.


http://www.pci.uni-heidelberg.de/tc/usr/bernd/downloads/blktrace/


Cheers,
Bernd