I am also affected by this regression.
It looks like Wheezy disables udev for md and uses an rc-script for assembling at boot; therefore it will not automatically assemble arrays after boot.
Trusty assembles real devices during and after boot, but seems to ignore virtual devices like /dev/md0.
So I added a new rule for virtual devices to the existing udev rules in Trusty. I created /etc/udev/rules.d/85-mdadm.rules with this single line rule:
This rule (plus the existing ones) assemble my nested raid during boot or any time later, but might not work for the root filesystem unless a initramfs-tools/hooks script is created (not tested).
I am also affected by this regression.
It looks like Wheezy disables udev for md and uses an rc-script for assembling at boot; therefore it will not automatically assemble arrays after boot.
Trusty assembles real devices during and after boot, but seems to ignore virtual devices like /dev/md0.
So I added a new rule for virtual devices to the existing udev rules in Trusty. I created /etc/udev/ rules.d/ 85-mdadm. rules with this single line rule:
SUBSYSTEM=="block", ACTION= ="add|change" , ENV{ID_ FS_TYPE} =="linux_ raid_member" , DEVPATH= ="*/virtual/ *", RUN+="/sbin/mdadm --incremental $tempnode"
This rule (plus the existing ones) assemble my nested raid during boot or any time later, but might not work for the root filesystem unless a initramfs- tools/hooks script is created (not tested).