Re: RAID device nomination (Feature request)

[Alex Elsayed <eternaleye@gmail.com>]

Hugo Mills wrote:

> On Thu, Apr 18, 2013 at 02:45:24PM +0100, Martin wrote:
>> Dear Devs,
<snip>
>> Note that esata shows just the disks as individual physical disks, 4 per
>> disk pack. Can physical disks be grouped together to force the RAID data
>> to be mirrored across all the nominated groups?
> 
>    Interesting you should ask this: I realised quite recently that
> this could probably be done fairly easily with a modification to the
> chunk allocator.
<snip>

One thing that might be an interesting approach:

Ceph is already in mainline, and uses CRUSH in a similar way to what's 
described (topology-aware placement+replication). Ceph does it by OSD nodes 
rather than disk, and the units are objects rather than chunks, but it could 
potentially be a rather good fit.

CRUSH does it by describing a topology hierarchy, and allocating the OSD ids 
to that hierarchy. It then uses that to map from a key to one-or-more 
locations. If we use chunk ID as the key, and use UUID_SUB in place of the 
OSD id, it could do the job.