What type of optical media is best for backing up just over 9 GB of data, leaving minimal unused space?

The best optical media for backing up just over 9 GB of data, while leaving minimal unused space, is DVD-10. This type of DVD has a capacity of approximately 8.5 GB on a single side, but it is actually a double-sided disc, which effectively doubles the storage capacity to around 17 GB total when both sides are used. Therefore, it is well-suited for your requirement of slightly over 9 GB, as it can accommodate that amount of data while still allowing additional space for future use if needed.

In comparison, a CD-R has a maximum capacity of about 700 MB, which is insufficient for a 9 GB backup. DVD-R also offers about 4.7 GB of storage per side, which again falls short for this requirement, while BD-R (Blu-ray Disc Recordable) provides a much larger capacity of approximately 25 GB for single-layer and 50 GB for dual-layer. However, choosing BD-R would result in significant unused space if only 9 GB is being backed up, making it less efficient for this specific task.