[Bug 1608495] Re: IMSM fakeraid handled by mdadm: unclean mounted volumes on shutdown/reboot

[Dimitri John Ledkov]

@john-center

I believe mdadm is already used by default during installation. However,
when reinstalling my desktop it was not smooth at all. It seems like
underlying devices got probed / mounted by something before mdadm-udeb
was available in the d-i and thus i had to manualy unmount things and
assemble the array from the d-i shell before continuing the
installation. Apart from that ftab / bootloaders  / initramfs / etc were
all setup correctly.

w.r.t. changing / updating udev rules. Things are odd on xenial vs later
releases, due to not using mdadm units correctly. =/ thus using offroot
is currently broken on xenial, where rootfs is on the intel matrix raid,
but I can double check if anything else can be improved.

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https://bugs.launchpad.net/bugs/1608495

Title:
  IMSM fakeraid handled by mdadm: unclean mounted volumes on
  shutdown/reboot

Status in mdadm package in Ubuntu:
  Fix Committed
Status in mdadm source package in Xenial:
  Fix Committed
Status in mdadm source package in Yakkety:
  Won't Fix
Status in mdadm source package in Zesty:
  Fix Committed

Bug description:
  Opening this report for Xenial and later as this problem does surface
  again due to moving to systemd.

  Background:

  mdadm is used to create md raid volumes based on Intel Matrix Storage
  Manager fakeraid metadata. The setup usually consists of a container
  set that contains one or more raid volumes. Which is the reason that
  those fakeraid volume are more affected by timing issues on
  shutdown/reboot.

  In my specific setup I am using one of the IMSM raid volumes as a LVM
  PV and one LV of that is mounted as /home. The problem is that
  unmounting /home on shutdown/reboot will update the filesystem
  superblock which causes the raid state to become dirty for a small
  period of time. For that reason with sysvinit scripts there is a
  mdadm-waitidle script which *must* be run after the umountroot (or for
  /home at least after umountfs) script has run.

  With Xenial both umountroot and umountfs are softlinks to /dev/null in /lib/systemd/system, so I am not sure they are good to cause the mdadm-waitidle to be delayed *after* all filesystems are unmounted.
  Practically I see that if /home is mounted on shutdown/reboot, the raid set will go into a full resync the next time I boot (additional pain but different problem: the resync appears to be much more aggressive than in the past, delaying boot a lot and rendering the system barely usable until it finishes). If I manually unmount /home before the reboot, the raid set is good.

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