One of the 4TB external USB hard drives I use for local backups started randomly disconnecting a few days ago. Today it failed completely. It’s a Seagate Backup Plus model, where the bottom of the enclosure consists of a small, removable shim that contains the USB & power connections and the USB to SATA converter chip. After trying different USB ports and cables without success, I decided to hook up the drive directly using SATA. After trimming a SATA cable with a utility knife to make it fit the narrow port opening, hooking it up, and rebooting… Finder offered to initialize an unreadable disk.
Disk Utility showed a single unreadable 500GB partition and a FAT partition table. The drive previously had a GUID partition table, not FAT. I have no idea what corrupted the disk in such an interesting way, but TestDisk was able to quickly scan the drive, locate the partitions and types, and repair everything in just a few seconds. The user interface hails from the 1990’s, but the software worked wonders and it’s completely free and open-source. It also runs on Linux, Windows, and DOS.
All my backups are intact and valid. I haven’t figured out what to do with the drive, though. Anecdotal evidence from the Internet suggests USB/SATA adapters are prone to failure, but I’m guessing the cause is probably cheap, poorly-designed power supplies. I’m not sure if it’s worth opening a support case with Seagate.