Common logical dumping algorithm used by Most UNIX systems
Maintains a bitmap indexed by i-node number with several bits per i-node
The algorithm operates in four phases:
1- begins at the starting directory .For each modified file, its i-node is marked in the bitmap. Each directory is also marked
2- unmarking any directories that have no modified files or directories in them or under them.
(phases 1 and 2 can be combined in one tree walk)
3- scanning the i‑nodes in numerical order and dumping all the directories that are marked for dumping.
(Each directory is prefixed by the directory’s attributes (owner, times, etc.) so they can be restored)
4- the files marked in phase 1 are also dumped, again prefixed by their attributes
Restoring a file system from the dump tapes is straightforward