By default, ZFS freezes I/O on ZVOLs when the underlying pool has failed. As a result, DRBD devices on top may get stuck: they can keep running and report UpToDate even though I/O is no longer progressing.
To prevent this, set the pool failmode to continue:
zpool set failmode=continue data
We should consider setting this flag automatically in the linstor ps cdp command and update the documentation accordingly.
cc @WanzenBug @ghernadi