[Bug 1635049] Re: Boot fails with degraded mdadm raid

[Kevin Lyda]

Hey there kids, this bug still appears to be relevant for 16.04. My
/dev/sda died today and I'm prepping to replace the disk. I note that
the answer here https://askubuntu.com/a/798213/185653 notes the missing
file and it's still missing.

I haven't tried a reboot as I'm waiting for the monthly check to
complete on the other array but I've added in that script and rebuilt my
initramfs and installed grub on sdb. Will let folks know how I get on.

The tone and comments in this bug from some reporters and others is...
poor. I would have hoped for better.

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https://bugs.launchpad.net/bugs/1635049

Title:
  Boot fails with degraded mdadm raid

Status in mdadm package in Ubuntu:
  Fix Released
Status in mdadm source package in Xenial:
  Fix Released
Status in mdadm package in Debian:
  Fix Released

Bug description:
  [Impact]

   * Systems fail to boot in certain status of mdadm arrays, requiring
  manual recovery / array assembly

   * Backport of boot logic from yakkety

  [Test Case]

   * Install a system with RAID1 and two hard-drives and boot the system with array in-sync
   * Shutdown
   * Disconnect one of the drives and thus boot, unexpectedly, degraded
   * The boot should complete.
   * Shutdown, and boot again, expecting degraded state.
   * The boot should complete.
   * Shutdown, reconnect disconnected drive, and boot again.
   * The boot should complete, add the device to the array, the array should be resyncing, and results with system with array in-sync, just like at the beginning of the testcase.

  [Regression Potential]

   * Systems may continue to fail to boot degraded.

  [Other Info]

   * Original report

  mdadm does not attempt to start partial md devices (incremental
  assembly) during initramfs and can cause system to fail to initramfs
  prompt if rootfs on md.

  http://askubuntu.com/questions/789953/how-to-enable-degraded-raid1
  -boot-in-16-04lts

  Fixed in debian mdadm 3.4-2: https://bugs.debian.org/cgi-
  bin/bugreport.cgi?bug=784070

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