Read this forum and you find many asking how to get their files back.

What you write works but many forget to backup their files. Externals are less reliable than most expected.

"At some time some of this material will be retired from my PC; but I may want to keep it on the portable version. Will that work?"

Until you drop the hard drive or it fails.

Parting thoughts. With Sky Drive giving your 25GB of free space and google docs giving quite a few GB why would I lose any document file today?