[RFC] Enhanced MD / alternatives in userspace

From: Carl-Daniel Hailfinger
Date: Fri Apr 16 2004 - 16:43:17 EST


during development of raiddetect I asked myself if this tool could be
extended to set up not only the classic vendor ATARAID devices, but also
things like Adaptec ASR (HostRAID) and DDF based RAID formats.

Raiddetect is a utility which searches all disks for known RAID
superblocks/metadata and parses the contents for validity. The results of
this scan can either be outputted to the console or used to tell dm/md to
set up the RAID devices. The newest version of raiddetect was posted to
linux-kernel a few minutes ago and I will provide a web home for it soon.

So far, the development of raiddetect is at a stage where I can find (and
mostly validate) the metadata of all ATARAID devices recognized by 2.4
kernels. Adding ASR and DDF detection should be relatively easy since I
tried to make the code moular and extensible.

Assuming the on-disk format of RAID5 et al. does not differ between the
Linux md implementation and e.g. DDF (modulo some offset and different
superblocks), DDF support is possible today with combinations of plain MD
and DM. No additional kernel code needed at all. Simply teach raiddetect
to understand the DDF metadata and pass this information to MD in a format
md understands. The DDF metadata can be masked away from MD by using DM so
you don't have to worry about it being trashed.

Since this is marked as [RFC], please comment on its (in-)feasibility.


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