Comment 11 for bug 1619844

It depends on what sort of raid modes are in place. If you are not using raid (e.g. RAID1) as provided by your motherboard firmware, and only use individual devices, it is best to disable raid settings in the bios and use regular acpi setting. I have to do this for example on latest generation of Dell XPS laptops that use "raid" mode on a single nvme drive with OS support drivers that are not available for linux.

Otherwise if you do use RAID controllers with mdadm, e.g. Intel Matrix RAID, DDF, etc. as part of https://bugs.launchpad.net/ubuntu/+source/mdadm/+bug/1722491 there is currently mdadm update available from xenial-proposed and zesty-proposed that might resolve this issue.

To test that solution please perform the following:

1) Install mdadm from xenial-proposed/zesty-proposed
   - See https://wiki.ubuntu.com/Testing/EnableProposed
   - Or download & install packages from
xenial
https://launchpad.net/ubuntu/+source/mdadm/3.4-4ubuntu0.1/+build/13596415
zesty
https://launchpad.net/ubuntu/+source/mdadm/3.3-2ubuntu7.5/+build/13596431

2) $ sudo apt install dracut-core

3) $ sudo systemctl enable mdadm-shutdown.service

4) $ sudo systemctl start mdadm-shutdown.service

After this the expectation is for shutdown/reboots to perform clean a shutdown, maintaining the raid array in a synced state, such that it comes up clean.

Please let me know if above resolves shutdown/reboot issues for you.

Regards,

Dimitri.