Re: nonstandard raid(4-ish) scheme

[John Robinson <john.robinson@anonymous.org.uk>]

On 24/01/2012 03:00, Lennert Buytenhek wrote:
> (I'm not on the list, please CC on replies.)
>
> Hi!
>
> While recently setting up a media server for a HTPC, I was wondering
> whether it'd be possible to set things up so that most disks can be
> kept spun down most of the time.
>
> Since the majority of the I/O on this sort of server is reads, the
> first idea was to store (directories of) media files entirely on
> individual disks, i.e. to not distribute them over all disks by
> striping, as that would require spinning up each disk on reads.  So,
> creating a large RAID(5/6) array out of all of the disks wouldn't be
> option here.
>
> RAID1ing pairs of disks would work, but this is somewhat wasteful,
> as it eats up half of your space.
>
> The ideal way of doing this would be to take N-1 disks out of your N
> disk set, and create separate filesystems on each of the disks, and
> store different sets of files on them, while using the last disk,
> disk N, as a parity disk of the N-1 data disks.
>
> This is equivalent to raid4 with the stripe size equal the size of
> one disk, and where the data disks get individual /dev/mdX entries
> instead of being concatenated into one large /dev/mdX.
>
> Would this be easy to implement?

I think it already has been, as UnRAID: 
http://en.wikipedia.org/wiki/Non-standard_RAID_levels#UnRAID

Cheers,

John.