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The map usedinomap is a list of inodes that have been deleted since the last dump. restore uses this map to delete files before doing a restore of files in this dump. The map dumpinomap is a list of all inodes contained in this dump. Each header contains a lot of information:

    Record type
    Dump date
    Volume number
    Logical block of record
    Inode number
    Magic number
    Record checksum
    Number of records to follow
    Dump label
    Dump level
    Name of dumped filesystem
    Name of dumped device
    Name of dumped host
    First record on volume
The record type field describes the information following the header. There are six basic record types:

     dump header
     Map of inodes deleted since last dump
     Map of inodes in dump
     Beginning of file record
     Continuation of file record
     End of volume marker

When dump writes the header, it includes a copy of the inode for the file or directory that immediately follows the header. Since inode data structures have changed over the years, and different filesystems use slightly different inode data structures for their respective

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filesystems, this would create a portability problem. So dump normalizes its output by converting the current filesystem's inode data structure into the old BSD inode data structure. This BSD data structure is written to the backup volume.

As long as all dump programs do this, then you should be able to restore the data on any Unix system that expects the inode data structure to be in the old BSD format. It is for this reason you can interchange a dump volume written on Solaris, HP-UX, and AIX systems.

This was first published in August 2007

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