-snip-
But since you're constantly swapping external drives, I'd recommend you to manually assign a letter that wont be used by the other drives, like Drive L~Z.
That's how I manage my external drives.
That way, even if you plugged the other drives first, the assigned letter for the external drive where the bitcoin datadir is, wont be taken by it.
To manually assign a drive letter:
- Go to search: "Create and Format Hard Disk Partition"
- Right-click on the disk that you want to change the letter and select "Change Drive Letter and Paths...".
- Highlight the letter, click "Change" and select the letter that you want from the drop-down menu, then "OK" to save it.
Then set the new custom datadir using the bitcoin.conf file in bitcoin's default data directory (location).
Edit it using a text editor and paste the line datadir=
If you don't have a bitcoin.conf file in the default data dir, you can create a new text document and rename it from "New Text Document.txt" into "bitcoin.conf" (including the extension '.txt' -> '.conf').