Re: md question re: max_hw_sectors_kb

[Bernd Schubert <bernd.schubert@itwm.fraunhofer.de>]

On 05/04/2011 07:58 PM, Martin K. Petersen wrote:
>>>>>> "Michael" == Michael Reed<mdr@sgi.com>  writes:
>
> Michael>  There is code in blk_queue_make_request() which lowers the
> Michael>  default value from INT_MAX to BLK_SAFE_MAX_SECTORS, which is
> Michael>  255.  This is generally lower than all the underlying devices
> Michael>  with which I use md.
>
> Yeah, the SAFE value is there to appease legacy low-level drivers.
>
>
> Michael>  As md appears to be a stacking driver, i.e., it calls
> Michael>  disk_stack_limits() for each member of a volume, it would seem
> Michael>  reasonable for md to use the, INT_MAX setting for
> Michael>  max_hw_sectors_kb instead of BLK_SAFE_MAX_SECTORS.
>
> Your fix is functionally correct. However, another case just popped up
> this week where we need to distinguish between stacking driver and LLD
> defaults. So I think we should try to handle this at the block layer
> instead of explicitly tweaking this knob in MD.
>
> I'll get this fixed up and will CC: you on the patch.
>

Could you please CC me or linux-raid as well? I have a similar patch for 
raid1 and while I'm not working on Lustre anymore, I know that Lustre 
also always has a another kernel patch for raid5...


Thanks,
Bernd