[Bug 1088464] Re: missing --incremental on array that is part of another array (nested)

[Launchpad Bug Tracker]

Status changed to 'Confirmed' because the bug affects multiple users.

** Changed in: mdadm (Ubuntu)
       Status: New => Confirmed

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https://bugs.launchpad.net/bugs/1088464

Title:
  missing --incremental on array that is part of another array (nested)

Status in “mdadm” package in Ubuntu:
  Confirmed

Bug description:
  http://www.spinics.net/lists/raid/msg40832.html

  > when booting, the system dumps
  > into initramfs shell with the raid array in an inactive state.

  There are two problems here.

  Firstly, the fact that the array doesn't assemble completely should not cause
  the boot to fail.  A degraded raid1 is perfectly sufficient for booting.

  What is happening is that the initrd is relying on udev to assemble the array
  by passing each new device to "mdadm --incremental $DEVNAME".
  This will assemble the array as soon as all devices are present, but not
  before.   If a device failed before shutdown that will be recorded in the
  metadata and "mdadm --incremental" will not wait for it.  If it disappears
  during reboot, mdadm will still expect it.

  To deal with this issue, the initrd should run
    mdadm --incremental --scan --run

            [better: only degrade the required raid, not all !!! ]

  
  which means "look for all arrays that are being incrementally assembled, and
  start them".
  This should be called after running "udevadm settle" and before mounting the
  root filesystem.

  However fixing this won't fix your problem [with a nested array], it
  will just change it.

  The udev rules files which is calling "mdadm --incremental" does so
  on /dev/sdb1 /dev/sdc1 and /dev/sde1, but apparently not on /dev/md0.

  If at the initrd shell prompt you run
    mdadm -I /dev/md0

  it should finish assembling md1 for you.  For some reason udev isn't doing
  that.

  Have a look in /lib/udev/rules.d or /etc/udev/rules.d for a file that runs
  "mdadm --incremental" or "mdadm -I" and see how it works.
  Maybe post it.

  BTW what distro are you using?

  NeilBrown

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