[Bug 1361842] Re: dmraid does not start on boot for single disk RAID0

[Phillip Susi]

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On 10/28/2014 09:55 PM, Jason Gunthorpe wrote:
> Fundamentally, if /dev/sda has a valid RAID label then it *MUST* be setup
> and accessed through the dmraid device and *NEVER* via /dev/sda.
> 
> Otherwise the installer will see a disc that is too big and it will destroy
> the RAID label at the end of the disc, then the system will not boot.

For MBR partitioned disks this isn't really a problem because they never
really use the last bit of the disk anyhow, but for GPT, yes... that
would be a problem.

> FWIW, RHEL gets this right and sets up dmraid on this disc.

Interesting.. they must have a patch that hasn't been upstreamed.


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https://bugs.launchpad.net/bugs/1361842

Title:
  dmraid does not start on boot for single disk RAID0

Status in “dmraid” package in Ubuntu:
  New

Bug description:
  I have a Lenovo server with a LSI controller that insists on having a
  RAID set to boot. So the BIOS is configured with a RAID0 stripe set,
  with a single disk:

  $ dmraid -i -si
  *** Group superset .ddf1_disks
  --> Subset
  name   : ddf1_4c5349202020202080861d60000000004711471100001450
  size   : 974608384
  stride : 128
  type   : stripe
  status : ok
  subsets: 0
  devs   : 1
  spares : 0

  Notice that 'devs' is 1.

  This causes this bit of code in dm-activate to bail:

          case "$Raid_Type" in
                  stripe)
                          if [ "$Raid_Nodevs" -lt 2 ]; then
                                  if [ -n "$Degraded" ]; then
                                          log_error "Cannot bring up a RAID0 array in degraded mode, not all devices present."
                                  fi
                                  return 2
                          fi
                          ;;

  Of course, the above is totally bogus, a 1 disk RAID0 is perfectly
  valid. I wonder if this should be testing 'status' instead?

  This is a problem because of GPT partitioning. If you don't start the
  RAID downstream tools will attempt to partition sda. The RAID metadata
  at the end of the disk collides with the GPT partition backup and it
  ends up destroying the RAID set and making the server unbootable. The
  kernel hints at this condition:

  [    4.202136] GPT:Primary header thinks Alt. header is not at the end of the disk.
  [    4.202137] GPT:974608383 != 976773167
  [    4.202138] GPT:Alternate GPT header not at the end of the disk.
  [    4.202138] GPT:974608383 != 976773167

  Which is 100% true, the GPT was written to the RAID, not the raw disk,
  and 974608383 sectors is at the end of the raid volume.

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