Re: raid1 mirror optimizations

[David Brown <david.brown@hesbynett.no>]

On 26/01/11 17:37, Oliver Brakmann wrote:
> On 2011-01-26 16:39, Roberto Spadim wrote:
>> i don't know what layout does, but, does raid1 have layout?
>
> No, only raid10 has different layouts.  For an explanation, see David's
> mail, or take a look at the Wikipedia entry for non-standard RAID
> levels, it illustrates the idea of the different layouts quite well,
> IMO: http://en.wikipedia.org/wiki/Non-standard_RAID_levels#Linux_MD_RAID_10
>

There are also different layouts for raid5 and raid6, though I don't 
think they make much difference unless you are doing something odd like 
trying to make your mdadm raid5/6 layout exactly match that of some 
hardware raid controller.  There are also special layouts that are used 
as intermediary steps in converting between raid5 and raid6 - you won't 
want to touch these.

So raid10 is the only level with /useful/ layout options.  The different 
options can make a measurable speed difference, with the best choice 
depending on the load.  The "far 2" layout is, I think, the best choice 
for common ready-heavy loads.