08-03-2011
A solution which I have used in 1980's backup solutions before there were much better commercial solutions.
Append archives on a tape by using the "no rewind" device. Make your first archive a simple text file containing the identity of the archive. Append your second and subsequent archives to the tape one-by-one with the "no rewind" device. Use the unix "mt" command to navigate the tape partitions. Read the first tape partition to check that you can access the the tape and that it is the correct tape.
Personally I would never use "tar" for any serious backup (but it has a use for cross-platform file copies).
If you don't have "large files" the unix "dump" and "restore" programs are what you should use if you don't have a proper commercial backup solution. These commands append backups of disc partitions to tape and allow restore of a whole partition or individual files. You can still have the first partition containing a simple text file to identify the tape.
To answer your original question you could use the unix "dd" command to read the first few blocks off the tape. The unix "head" command (on a tape device not the output from a "tar" archive contents list) is totally irrelevant because this is a tape device is not a text file.
Last edited by methyl; 08-03-2011 at 07:35 PM..
Reason: Assorted typos
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LEARN ABOUT DEBIAN
dds2index
dds2index(1) General Commands Manual dds2index(1)
NAME
dds2index - tool to create an indexfile for the use of
SYNOPSIS
dds2index [options]
DESCRIPTION
dds2index creates an index file that is required by the file extraction utility dds2tar(1). It works on tar archives stored on dds tape
devices (DAT). Since the file structure of the tape archives is used to extract the files, the archive must be an uncompressed tar ar-
chive. But compression by the transparent signal processor of the tape device is allowed.
The index created by dds2index is written to stdout by default and should normally be stored on hard disk as indexfile for later use by
dds2tar(1).
The default tape device to read from is /dev/nst0, which may be overridden with the environment variable TAPE, which in turn may be over-
ridden with the -f device option. The device must be a SCSI tape device.
OPTIONS
-f devicefile
device of the tape archive. Must be a character special file.
-t indexfile
write the index to indexfile, not to stdout.
-z,--compress
write the index in (gzip) compressed mode.
--help print some screens of online help with examples through a pager and exit immediatley.
OPTIONS you didn't really need
-b, --block-size
Set the maximal blocksize, dds2index can handle.
--z, --no-compress
Don't filter the archive file through gzip.
-v,--verbose
verbose mode. Print to stderr what is going on.
-h,--hash-mode
Print a hash sign '#' to stderr for each MB read from tape.
-V,--version
Print the version number of dds2index to stderr and exit immediately.
EXAMPLES
Example of getting the index from the default tape /dev/nst0 and storing it in file archive.idx:
dds2index -v -t archive.idx
WARNING
This program can only read records (tar is calling them tape blocks) up to 32 kbytes. A bigger buffer will cause problems with the Linux
device driver.
ENVIRONMENT
The environment variable TAPE overrides the default tape device /dev/nst0.
FILES
/dev/nst0 default tape device file. Must be a character special file.
SEE ALSO
dds2tar(1), mt(1), mt-dds(1), tar(1), gzip(1)
HISTORY
This program was created as a tool for dds2tar(1).
AUTHOR
J"org Weule (weule@cs.uni-duesseldorf.de), Phone +49 211 751409. This software is available at ftp.uni-duesseldorf.de:/pub/unix/apollo
2.4 dds2index(1)