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

[fermulator]

Just attempted this without much thinking:
http://pastebin.com/eWy2n0hq

Similar situation as reported by b-candler.

Upon reboot after that, the system root drive was /dev/sda ,/dev/sdb
unused.

If I try to force an mdadm assemble, it only pulls in /dev/sdb since sda is in use by the operating system.
{{{
callaghan at callaghan-family:/dev/disk$ cat /proc/mdstat 
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
md126 : inactive sdb[0]
      62520452 blocks super external:/md127/0
       
md127 : inactive sdb[0](S)
      2260 blocks super external:imsm
}}}

I also tried to run "update-grub", but afterwards I can see that
/etc/grub/grub.cfg is now set to boot from /dev/sda (by-uuid), not any
mdadm.

Somehow need to get "update-grub" to reconfigure for mdadm/mdraid
support.

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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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