G-Raid not mounting on iMac, but mounts on MacBook Air

Howdy gang,

I’m new here. I have a Thunderbolt G-Raid drive that suddenly stopped mounting on my iMac. In truth, it’s the other way around - the iMac won’t mount the drive. I tried doing the usual PRAM and SMC stuff with no help.

This problem seems to have happened suddenly after connecting the drive to my MacBook Air using the Thunderbolt to USB-C adapter. The drive still mounts on the Air, just not on the iMac.

The iMac is the last model that didn’t have the hybrid drive (I can’t remember what it’s called) so I guess it’s a Thunderbolt 2. I didn’t see anything in the System Report that was a clear indicator (to me at least) of the Thunderbolt type.

The iMac is running El Capitan 10.11.6 and the MacBook is running Catalina 10.15.2.

Any ideas what might be wrong and what the fix might be?