A duplexed backup set uses the same number of SBT channels as a non-duplexed backup set for the same number of files.

A non-duplexed backup set written to disk can be duplexed to disk by backing up the backup set that is already on disk.

A non-duplexed backup set written to SBT can be duplexed to tape by backing up the backup set that is already on tape.

A non-duplexed backup set written to disk can be duplexed to tape by backing up the backup set that is already on disk.

A non-duplexed backup set written to SBT can be duplexed to disk by backing up the backup set that is already on tape.

A duplexed backup set always uses twice as many SBT channels as a non-duplexed backup set for the same number of files.