[RFC/CFT] Trusty work for dmraid

[Stefan Bader]

We had been discussing some changes to dmraid at the last vUDS[1]. One part was
to move Intel Matrix Storage Manager (IMSM) fakeraid users over to mdraid. The
other part was to verify whether we can stop using dm-raid45 (which is a special
module the ubuntu kernel ships but has not been maintained for a while) and make
dmraid use the dm-raid module instead (this one is included in the upstream kernel).

I have prepared changes for both[2] which did work for IMSM (before I disabled
support) and a RAID5 I had there. Currently there would only be one drawback
which is that cases which store meta-data at the beginning of a disk and data
after that would not work. But I am not sure whether there are cases out there
that work like this.

The support for RAID4 and RAID5 in dmraid also is rather limited:
ddf1    : SNIA DDF1 (0,1,4,5,linear)
nvidia  : NVidia RAID (S,0,1,10,5)
[isw    : Intel Software RAID (0,1,5,01)]

So practically the only setups to worry are NVidia controllers supporting RAID5
and those using DDF1 using RAID4 or 5. Are there people out there which have
BIOS-/fakeRAID configs enabled for RAID4 or 5 and currently use dmraid to set
those up under Linux?
One alternative option would be to check whether mdadm DDF support also includes
everything that dmraid did. At least a quick test with a ddf1 RAID5 which I did
set up using mdadm seems to be found by dmraid scanning, too.
That option would leave us only with NVidia controllers depend on dmraid RAID5.

-Stefan

Btw, to make mdadm automatically add the IMSM RAID I have to add the following
line to /lib/udev/rules.d/64-md-raid.rules:

 # handle potential components of arrays (the ones supported by md)
 ENV{ID_FS_TYPE}=="linux_raid_member", GOTO="md_inc"
+ENV{ID_FS_TYPE}=="isw_raid_member", GOTO="md_inc"
 GOTO="md_inc_skip"

[1] https://blueprints.launchpad.net/ubuntu/+spec/core-1311-dmraid2mdadm
[2] http://people.canonical.com/~smb/dmraid-conversion.debdiff

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