Marlier, Ian wrote:
Because /dev/hd[ab]1 is larger than /dev/md0, and the starting block of the partitions is the same, the filesystem should remain intact.
So you are saying that the filesystem was less than 16GB in size to start with?
However, upon rebooting, I ran into a problem. /dev/md0 cannot be mounted because of a problem with the superblocks.
Right, the superblocks would have been between 64KB and 128KB from the end of the original md device, which presumably was ~33GB in size. Now that the partitions are smaller, the superblocks are no longer located inside of the partitions, so the new partitions effectively have no superblocks.
I figure that something needs to be done with mdadm to get it to
recognize the "new" /dev/hda1 and /dev/hdb1 as /dev/md0 -- but I don't
want to do a mdadm --create because that will overwrite the filesystem
already on the disks (I think?).
Create will write new superblocks to /dev/hda1 and /dev/hdb1. Without these, the array cannot be started. The superblocks are what tell the md driver that /dev/md0 is composed of /dev/hda1 and /dev/hdb1.
If the filesystem is at least 128KB smaller than the partitions, then you'll have room for the superblocks at the end. Otherwise, go back with fdisk and make the partitions just a little bit larger and then do your mdadm --create.
Is this something that mdadm --assemble can do? If so, what switches need to be fed to the command?
Assemble requires that the superblocks already be present, so until they are re-created, you cannot assemble the array.
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