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dump rescans all the inodes and specifically looks at directory inodes that were found in Pass I to determine whether they contain any of the files targeted for backup. If not, the directory's inode is dropped from the list of directories that need to be backed up.
By deleting in Pass IIa directories that do not need to be backed up, the parent directory may now qualify for the same treatment on this or a later pass, using this algorithm. This pass is a rescan of all directories to see if the remaining directories in the directory inode list now qualify for removal.
Directories were dropped in Pass IIb. Perform another scan to check for additional directory removals. This ends up being the final Pass II scan because no more directories can be dropped from the directory inode list. (If additional directories had been found that could be dropped, another Pass II scan would have occurred.)
This is when dump actually starts to write data. Just before Pass III officially starts, dump writes information about the backup. dump writes all data in a very structured manner. Typically, dump writes a header to describe the data that is about to follow, and then the data is written. Another header is written and then more data. During the Pre-Pass III phase, dump writes a dump header and two inode maps. Logically, the information
TS_TAPE dump header
A map of inodes deleted since the last dump
A map of inodes in the dump
This was first published in August 2007