Possibly recover a missing RAID stripe

Jul 18, '05 09:27:00AM

Contributed by: mosatch

My striped RAID disappeared tonight. All I would get on boot, or when plugging in the FireWire cable, was an error message that my disk format was not recognized. Looking in Disk Utility, one of the disks in the stripe was still listed under the RAID and was still listed as having a partition. The other member of the RAID, though, did not list any partitions at all in Disk Utility.

Running diskutil list from the command line confirmed that there was no partition map on the bad disk. Running pdisk from the command line, then issuing an L further confirmed the lack of a partition map.

Because this is a mirror, it was a safe assumption that the map on this disk should be the same as on the other disk in the mirror. Using pdisk, I initialized the partition map on the bad disk (by typing i), then created each entry in the partition exactly as on the other disk. After writing the updated partition map, the disk partition magically reappeared in Disk Utility, and the RAID came back up. Data was still there and everything was still accessible.

I'm not sure how the partition map got corrupted, but if you've got no hope of recovering your stripe, give this a try.

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