== A gotcha with the format of _dump_ archives

Most archive formats, such as tarballs, cpio archives, and zip archives,
interleave the file names (and their directory structure) with the file
contents. The _dump_ filesystem backup program such as Solaris _ufsdump_
do not. The dump archive format starts with an index that has all of the
filenames and the directory structure; after this comes the actual file
content, labeled by inode number.

This has an important consequence for detecting damaged archives. In an
interleaved format like a tarfile, getting a full file listing requires
reading the entire archive and thus checks that it's intact. However, in
_dump_'s format getting a full file listing only requires reading the
first bit of the archive; it does not guarantee that anything past the
index is uncorrupted or that all of the listed files are actually present
in the archive.

There are two ways of verifying _dump_ archives; one is general and
the other requires the Linux version of _restore_.

* Linux's _restore_ has a _-N_ flag that causes it to not write
  anything to disk, so you can do a 'dryrun' restore that reads
  the entire archive with something like _restore -x -o -N -f ..._.

  Linux's _restore_ can generally read the output of _dump_ from
  non-Linux systems. In particular, we have tested it with
  Solaris 8 _ufsdump_ and it works fine.

* you can use a full file index to work out the highest inode
  number in the dump archive and then restore just it. Because _dump_
  usually writes out files by increasing inode number, this generally
  forces the restore program to read the entire archive.

  (However, I don't know if this will detect missing files,
  things that are in the index but not in the file contents.)

If neither of these are workable or good enough, your only option is to
do a full restore to a scratch partition somewhere.

(For reference, the home of the Linux _dump_ and _restore_ is [[here
http://dump.sourceforge.net/]]. While _dump_ requires ext2 specific
header files and libraries, I believe that _restore_ can be compiled on
most any system with some work.)