External drives · Drive formats
Why does one external drive show up as two drives on my Mac?
Short answer: The drive is divided into more than one volume or partition, and each appears as its own drive. Check how it's split in Disk Utility (View → Show All Devices); you can remove an unwanted, empty volume there.
The drive has more than one volume or partition, and each one appears in Finder as its own drive. That's normal if you (or the manufacturer) set it up that way — for example a separate Time Machine volume, or a small partition holding the maker's software.
Open Disk Utility with View → Show All Devices to see how the drive is divided. If a second volume is unwanted and empty, you can delete it there and its space returns to the others (APFS volumes) or can be merged back (partitions). See adding or removing volumes.