Given that the MBP607SP-B is one of the older models, I'm hoping that a replacement backplane is still available. Drives are active and LEDs light up with activity but drives in the 2 slots on the left generate a lot of read/write errors. It's fairly obvious when I create a ZFS pool of 4 drives and the drives in those slots (and only those slots) register a lot of read/write errors when I copy a good amount (several hundred GiB) of files to the pool and I run a zpool status. I've tested it thoroughly to isolate the problem (various combinations of drives, 1, 5 and 6 disk ZFS pools, with a second dock in the mix) and it's only the disks in those slots that show errors. I bought the item from Amazon in 2019 so I presume it's still in warranty.