Going by the documentation here

When checking out a new package, get creates the target directory GOPATH/src/. If the GOPATH contains multiple entries, get uses the first one. For more details see: 'go help gopath'.

Further it describes each flag and none of them seem to allow you to change the download directory.

It kinda makes sense in that it removes complexity and the fact that if you're using modules primarily - changing GOPATH should be pretty seemless.

My suggestion, provided you're using go modules, would be to just change your GOPATH env variable to point to your newly mounted storage device. This will:

1. Re-Download all your dependencies in all your golang projects when you build or go mod tidy them
2. If you use remote tools and used this server as you dev env - you would need to run go mod tidy for each project to prevent code editors and IDEs from screaming error at you.
3. If you choose to delete the old GOPATH directory - make sure your new GOPATH/bin is in PATH - and you would need to re-install any binaries you may have installed there.