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Symbolics tape inefficiencies

    Date: Wed, 27 Sep 89 11:33:01 EDT
    From: charles@nynexst.com (Charles Jankowski)
    Has anyone formally looked into the relative space efficiencies
    of Symbolics tape facilities (LMFS dump and carry tape especially)
    as compared to comparable UNIX programs like dump and tar? It seems
    to me that the Symbolics are incredibly inefficient. Has anyone else
    noticed this? Does anyone know why this might be so?


    Charles Jankowski
    NYNEX Science and Technology

Yes I have observed this vs. a Sun tar tape.

It seems that the secret to highly efficient tar tape usage is to
declare a large block size and then many small files are included into
one block.  The large block is then written to the tape with no "inter
record gaps" as a single record.

Symbolics on the other hand, will only put one file in a record.  Thus
if you have many small files you get lots of IRGs.  I think IRGs are
fairly large, like 0.75 inches, and a 200 hundred byte file would be
only 0.16 inches on a 10,000 bits/inch tape.

It is also possible that Symbolics writes extra records containing file
directory records, but I am not sure of this.

In any event, if symbolics where to go to a (long) fixed-length record
format and pack multiple files into the records, the tapes could hold
much more data.