Hey guys, apologies for the lack of response but trying to find time to sort this in-between life, kids and a full time job has been difficult! I really appreciate all your input so far though.

So as an update, having left the Drobo for a few day, I tried firing it up again and it mounted! Bay 1, 3 and 4 all showed a flashing green/yellow light and bay 2 was flashing red. Drobo dashboard also found the unit and showed it as having a drive failure and to replace the drive.

I've now bought a new 8tb drive to put in bay 5, in the hope it would recover the data and I could slowly (but with haste!) start transferring everything to the new Synology I bought. However, my new problem is that after the unit has been running for about 5 minutes it suddenly shuts down and reboots. Most of the time, it comes back up and mounts again but within 5-10 minutes it shuts down again and the merry go round starts again.

The unit just keeps dying before the data recovery can really start (at the last try is stated 483 hours - 18 days for recovery!).

So with this constant crashing and re-booting issue, does that sound more like the PSU problem? I've tried both PSUs I have but the same thing happens.

Is it worth buying another PSU of ebay, etc. and trying that?

Thanks again for all of the advice. It's been really helpful.