Section 8.7. Disk-to-Disk-to-Tape Backup

8.7. Disk-to-Disk-to-Tape Backup

A very important methodology in today's backup systems is to first back up data to disk, and then copy it to tape. This is referred to as disk to disk to tape, or D2D2T. As long as the backup product can support automatically copying data from one media type to another, it can be used to support D2D2T backups. However, support for automating staging based on capacity can help a lot.

For example, suppose you back up to a large disk array or virtual tape library (discussed in detail in Chapter 9), and you would like backups to stay on that VTL as long as possible before being moved to tape. The ideal would be that the backup software would automatically copy the backups from disk to tape, and would automatically expire the disk-based backups to make room for more backups. This kind of functionality is often called disk staging and is usually only available if you are backing up to a filesystem (i.e., not using a VTL).

Different backup software companies support D2D2T in a number of different ways, and some of them are more fond of it than others. If you are a fan of D2D2T, you should definitely look into how well the backup software you are considering supports the features in this area.