When the metadata is at the start of the device, it is possible that it
describes a device large than the one it is actually stored on. When
this happens, report it loudly in --examine.
....
Unused Space : before=1968 sectors, after=-2047 sectors DEVICE TOO SMALL
State : clean TRUNCATED DEVICE
....
Also report in --assemble so that the failure which the kernel will
report will be explained.
mdadm: Device /dev/sdb is not large enough for data described in superblock
mdadm: no RAID superblock on /dev/sdb
mdadm: /dev/sdb has no superblock - assembly aborted
Scenario can be demonstrated as follows:
mdadm: Note: this array has metadata at the start and
may not be suitable as a boot device. If you plan to
store '/boot' on this device please ensure that
your boot-loader understands md/v1.x metadata, or use
--metadata=0.90
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md/test started.
mdadm: stopped /dev/md/test
Unused Space : before=1968 sectors, after=-2047 sectors DEVICE TOO SMALL
State : clean TRUNCATED DEVICE
Unused Space : before=1968 sectors, after=-2047 sectors DEVICE TOO SMALL
State : clean TRUNCATED DEVICE