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We had been discussing some changes to dmraid at the last vUDS. 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 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.
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)