If you don’t use Time Machine, you might notice that every time you attach a new and/or blank hard disk to the computer you get asked if you want to use it for backups. Here’s a simple trick that will stop that happening.
You can stop this request dialog box from appearing by opening a Terminal window (Finder -> Applications -> Utilities – > Terminal) and typing the following:
defaults write com.apple.TimeMachine DoNotOfferNewDisksForBackup -bool TRUE
Then log out and back in again for the changes to take effect.
If you’d like to restore the request dialog at a later date, again open Terminal then type the following (log out and back in again after for the changes to take effect):
defaults delete com.apple.TimeMachine DoNotOfferNewDisksForBackup