[Bug 259145] Re: degraded NON-root raids never --run on boot

[Dmitrijs Ledkovs]

we don't know which raids are required for rootfs, but using deduction,
once rootfs did appear we know which raids were not required.

So we could for each incomplete non-rootfs raid do:
mdadm --remove <incomplete-md-device> <arbitrary-member-device-of-incomplete-array>
mdadm --incremental --run <arbitrary-member-device-of-incomplete-array>

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https://bugs.launchpad.net/bugs/259145

Title:
  degraded NON-root raids never --run on boot

Status in “mdadm” package in Ubuntu:
  Confirmed
Status in “mountall” package in Ubuntu:
  Invalid

Bug description:
    Systems with say /home on raid won't come up booting when raid was
  degraded during downtime.

  An init script like /etc/init.d/mdadm-degrade - or because of already
  doing that kind of watchdog functionality - "mountall" needs to --run
  particular necessary arrays (those with fstab bootwait) degraded if
  they don't come up complete after a timeout.

  Because the proper mdadm --incremental mode command is not available
  (Bug #251646) a workaround needs to be used:

  mdadm --remove <incomplete-md-device> <arbitrary-member-device-of-
  incomplete-array>

  mdadm --incremental --run <arbitrary-member-device-of-incomplete-
  array>

  (See https://wiki.ubuntu.com/ReliableRaid "mountall" functionality
  related:" about determining the md devices that the devices mentioned
  in fstab depend on.)

  
  ---

  The possibility that large server RAIDs may take minutes until they
  come up, but regular ones are quick, can be handled nicely:

  
        "NOTICE: /dev/mdX didn't get up within the first 10 seconds.

        We continue to wait up to a total of xxx seconds complying to the ATA
        spec before attempting to run the array degraded.
        (You can lower this timeout by setting the rootdelay= parameter.)

        <counter> seconds to go.

        Press escape to stop waiting and to enter a rescue shell.

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