About MSDP container files
The deduplication storage implementation allocates container files to hold backup data. Deleted segments can leave free space in containers files, but the container file sizes do not change. Segments are deleted from containers when backup images expire and the NetBackup Deduplication Manager performs clean-up.
The NetBackup Deduplication Manager checks the storage space every 20 seconds. It then periodically compacts the space available inside the container files. Therefore, space within a container is not available as soon as it is free. Various internal parameters control whether a container file is compacted. Although space may be available within a container file, the file may not be eligible for compaction.