Re: The missing RAID level

From: Junio C Hamano
Date: Wed Apr 21 2004 - 16:53:51 EST

>>>>> "HT" == Hubert Tonneau <hubert.tonneau@xxxxxxxxxxxxxx> writes:

HT> So, one very interesting possibility would be to have an
HT> extra RAID level that would do the following:

HT> assuming that you connect 5+1 partitions, then you get 5 md
HT> partitions, not a single one, with the following properties:

HT> . any read to mdX goes straight forward to reading the
HT> underlying partition.

HT> . any write goes staight forward to writting the underlying
HT> partition, but also updates the parity on the extra
HT> partition.

It seems to me that you can create a single RAID-4 device out of
5 data and 1 parity disks, and run device mapper on top of that
RAID-4 device, picking every 6 chunk worth of data and
collecting into a device (totalling 6 devices). The first 5
such device mapper devices would end up with blocks from the
underlying 5 data disks. I do not know offhand if such a dm
target already exists, though.

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