[Bug 1028677] Re: mdadm should be used for fakeraid (instead of dmraid)

[Brian Candler]

I have a 12.04 system with fakeraid for the root partition across
/dev/sda and /dev/sdb. I want to convert it from using dmraid to mdadm
(so I can monitor it with /proc/mdstat for instance)

mdadm is 3.2.5, and it says in the manpage it can understand ddf and
imsm metadata, and this indeed seems to be the case:

# mdadm --examine /dev/sda
/dev/sda:
          Magic : Intel Raid ISM Cfg Sig.
        Version : 1.1.00
    Orig Family : 8bc6b015
         Family : 8bc6b015
     Generation : 00000010
     Attributes : All supported
           UUID : 2ff8e106:4db45609:75487070:XXXXXXXX
       Checksum : b92d117e correct
    MPB Sectors : 1
          Disks : 2
   RAID Devices : 1

  Disk00 Serial : S14CNEAXXXXXXXX
          State : active
             Id : 00000000
    Usable Size : 234435342 (111.79 GiB 120.03 GB)

[Volume0]:
           UUID : a7fb0d20:01efbd85:c89e3f79:bf86cf8e
     RAID Level : 1
        Members : 2
          Slots : [UU]
    Failed disk : none
      This Slot : 0
     Array Size : 222715904 (106.20 GiB 114.03 GB)
   Per Dev Size : 222716168 (106.20 GiB 114.03 GB)
  Sector Offset : 0
    Num Stripes : 869984
     Chunk Size : 64 KiB
       Reserved : 0
  Migrate State : idle
      Map State : uninitialized
    Dirty State : clean

  Disk01 Serial : S14CNEAXXXXXXXX
          State : active
             Id : 00000001
    Usable Size : 234435342 (111.79 GiB 120.03 GB)

(Ditto for sdb)

So to try and migrate it, I did the following:

* apt-get remove dmraid   # removes udev rules for dmraid
* apt-get autoremove
* /usr/share/mdadm/mkconf >/etc/mdadm/mdadm.conf

mdadm.conf has two relevant lines:
ARRAY metadata=imsm UUID=2ff8...
ARRAY /dev/md/Volume0 container=2ff8... member=0 UUID=...

However on bootup, the root filesystem came up as /dev/sdb1, so it looks
like mdadm didn't auto-detect the arrays.

I also tried "md=1 raid=autodetect" on the kernel command line, to no
avail (although the root filesystem came up as /dev/sda1 in that case;
it may have been a coincidence)

Putting dmraid package back again, the system said it was unable to find
the root device with the given UUID, and panicked. So now I have to
specify root=/dev/sda1 explicitly.

I was kind-of expecting to break the system this way as I was planning
to reinstall it anyway, but it would be great to know how to reinstall
it so that it uses mdadm raid1 for its root but with BIOS-compatible
metadata.

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https://bugs.launchpad.net/bugs/1028677

Title:
  mdadm should be used for fakeraid (instead of dmraid)

Status in “debian-installer” package in Ubuntu:
  Invalid
Status in “mdadm” package in Ubuntu:
  Invalid
Status in “partman-md” package in Ubuntu:
  Confirmed
Status in “ubiquity” package in Ubuntu:
  Invalid

Bug description:
  mdadm now support external metadata and can hadle fakeraid better than dmraid:
  https://raid.wiki.kernel.org/index.php/RAID_setup#External_Metadata
  http://download.intel.com/design/intarch/PAPERS/326024.pdf

  It seems that dmraid is no more developed (only maintenance), so
  ubuntu should use mdadm instead of dmraid for fakeraid.

  Actually, it's not possible to setup a new ubuntu install with mdadm
  fakeraid (tried 12.04 and 12.10 alpha 2 alternate cd): only dmraid is
  offered.

  ProblemType: Bug
  DistroRelease: Ubuntu 11.10
  Package: mdadm (not installed)
  ProcVersionSignature: Ubuntu 3.0.0-23.39-generic 3.0.36
  Uname: Linux 3.0.0-23-generic i686
  NonfreeKernelModules: nvidia
  ApportVersion: 1.23-0ubuntu4
  Architecture: i386
  Date: Wed Jul 25 00:45:56 2012
  InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release i386 (20111011)
  ProcEnviron:
   LANGUAGE=en_US:en
   PATH=(custom, no user)
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: mdadm
  UpgradeStatus: Upgraded to oneiric on 2012-07-07 (17 days ago)

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