After-image extents contain a series of notes grouped together into after-image blocks. In the event of a source database failure, you can use the after-image extents with the database roll-forward recovery process to restore the source database to its pre-failure condition, without losing completed transactions that occurred since the last database backup.

There are two after-image extent types—fixed-length or variable-length— and there are five after-image extent states—empty, busy, locked, full, or archived.