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

[Namhyung Kim <namhyung@gmail.com>]

Namhyung Kim <namhyung@gmail.com> writes:
> 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. :(
>

I'm confused again. If fo > 0 && fc > 1 && nc > 1 then it turns out to
a near array with reduced size, no? Does it still need to be treaded
as RAID0?


> 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.
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