vax/vms file archival ideas and suggestions

John A. Dundas III dundas at caltech.edu
Thu Oct 19 17:19:14 CDT 2006


At 3:13 PM -0600 10/19/06, Richard wrote:
>In article <a06230902c15d8d43781e@[131.215.234.40]>,
>     "John A. Dundas III" <dundas at caltech.edu>  writes:
>
>>  If on the other hand the files are more important (than being able to
>>  recreate the tape exactly), [...]
>
>What would require an exact tape image, as opposed to files and their
>contents?

Tapes where retention of attributes, block sizes, placement, etc., 
are just as important as (maybe more so than) the file contents.  Two 
things come to mind:

1) a simulator (SIMH, Charon, etc.) where you wanted to work with a 
(virtual) tape device.  Pat mentioned booting an OS tape; absolutely.

2) the ability to recreate the tape (either on the same media, TK50 I 
think was this case, or other media 9-track, TK70, etc.).

If I copy files from tape to disk, I lose all blocking information 
(there might be different block sizes on the tape for different 
files).  I won't be able to recreate the tape from the files 
themselves without additional meta information.  Boot tapes often 
(sometimes?) contain boot data/code outside of recognizable file 
headers or marks on the tape.  I believe the early PDP-11 tapes were 
this way.  I can tell you that later PDP-11 (RSTS) tapes are 
multi-format, i.e., the first few (maybe dozen) files are DOS-11 
format, including the boot file, then the rest of the tape is written 
in ANSI format.  IIRC, DEC's Unix-11 V7m contained boot information 
at the front of the tape, then several tar images separated by tape 
marks on the remainder.  A tape image is able to capture this sort of 
information in addition to the file data itself.

John



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