I'm trying to recover a My Book Duo (the older rounded shape one), the unit was kicked, both drives got a 99% recovery.

I know the bridge board runs encryption, but when I put the two clone drives back into the unit it doesn't recognise the RAID 0 configuration and just wants to set it up again.

Do the exact same model drives need to go back in the unit, or can any WD drive do? And does the encryption key stored in the original drive's firmare need to transplanted into the clone drives?

Assuming you don't get any answer to your questions, I would ...

1/ dump the SPI flash on the bridge PCB.

2/ examine the partition metadata on each drive to see whether there is a reserved area at the end of the UA (for use by the bridge firmware).

3/ scan the OS partitions for HDD serial numbers or model numbers or WWNs.

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A backup a day keeps DR away.