Re: [PATCH v2 1/5] md/raid10: optimize read_balance() for 'far offset' arrays

[Namhyung Kim <namhyung@gmail.com>]

2011-06-15 (수), 08:51 +0200, Keld Jørn Simonsen:
> On Wed, Jun 15, 2011 at 11:02:00AM +0900, Namhyung Kim wrote:
> > If @conf->far_offset > 0, there is only 1 stripe so that we can treat
> > the array same as 'near' arrays.
> 
> does it also work with more than 2 copies - eg 3 copies?
> I think the original code just takes the available data blocks with the 
> lowest address.
> 

Hi,

Let me clarify this: AFAIK, 'far offset' array saves redundant data in
the diagonally adjacent chunk/disk, so it could be roughly thought as
'raid0' array with reduced size - just ignore redundant chunks here. It
was my mistake considering it as 'near' array. :(

Therefore, it makes more sense distributing reads over the array based
on some criteria - here, the address of starting sector - like RAID0
does. Now I see that the same goes to the 'far copies' array exactly, so
the original code is correct.

Thanks.


-- 
Regards,
Namhyung Kim


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