There's a technique called active spare, and is already available on
some hardware RAID controllers. It keeps the hot spare in sync with
the array, such that in an event of a disk failure, the spare kicks-in
immediately without wasting time for a resync.
I think what you're proposing is similar to the following scenario:
array0: (assume raid5): disk0, disk1, disk2, disk3(spare)
array1: (raid1): disk0, disk3
Though I'm not sure if it's feasible to nest raids or have a disk to
be a member of 2 arrays at the same time.
I think it was proposed before, but I donno about its priority.
2010/1/25 Michał Sawicz <michal@xxxxxxxxxx>:
> Hi list,
>
> This is something I've discussed on IRC and we achieved a conclusion
> that this might be useful, but somewhat limited use-case count might not
> warrant the effort to be implemented.
>
> What I have in mind is allowing a member of an array to be paired with a
> spare while the array is on-line. The spare disk would then be filled
> with exactly the same data and would, in the end, replace the active
> member. The replaced disk could then be hot-removed without the array
> ever going into degraded mode.
>
> I wanted to start a discussion whether this at all makes sense, what can
> be the use cases etc.
>
> --
> Cheers
> Michał (Saviq) Sawicz
>
--
Majed B.
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