Dell Storage Manager 2020 R1 Administrator's Guide

Incremental Backups

Each time a backup is performed, the NDMP server stores the timestamp for the backup. When the NDMP server performs an incremental backup, it uses the timestamp stored for the previous full or incremental backup to determine if a directory or file needs to be included.

Both supported backup types (dump and tar) support incremental backup. The algorithm for traversing the backup target directory is the same. However, because inode-based file history generation has different requirements to support DAR, the backup data stream generated is different:

• dump: Each directory visited will be backed up and a file history entry will be generated. It does not matter whether the directory has changed.
• tar: Backs up and generates a file history entry only for the directories that have changed.

Therefore, the amount of data backed up using a tar backup will be less than that of a dump backup. The size difference depends on the number of directories in the backup data set.