Dumping to an exabyte tape drive

[Brian Hackworth]

In article <776PKVH at dri.com>, braun at dri.com (Kral) writes:
|> In article <439 at cfa.HARVARD.EDU> wyatt at cfa.HARVARD.EDU (Bill
Wyatt,OIR) writes:
|> >
|> >I think you'd better concede the last 10% or so, as long as dump
can't deal
|> >with EOT. And even if it could, I once had a nasty surprise when
restore
|> >broke because a multi-volume dump (9-track in this case) did't start
at the
|> >beginning of the tape. 
|> >
|> 
|> So the $64k question now is: why can't dump properly deal with end of
tape?
|> It's not like it's a new technology or something.
|> 
|> Another (I suppose this one is only an $8k question): I'm not sure
what you
|> mean about the multi volume set above?  How did dumps behavior cause
the multi
|> volume dump to start not at BOT?
|> 

This whole discussion points out two serious flaws in the BSD dump:

    1. It doesn't handle end-of-tape.  You're right, this isn't new
       technology.  It is fairly hard to add to dump, though, due to
the
       way the program is designed.

    2. Adding new devices, especially high-capacity cartridge drives,
       is difficult because you must figure out how to trick dump
       into giving correct estimates.

For DG's version of dump, we have rewritten BSD dump to address these
issues (and others) by (a) recognizing and sanely handling EOT,
and (b) providing a table of dump devices which lists a name
for the device, the blocking factor, and the capacity (such
as "150M" or "2.2G").

Together, this allows you to add one line to one file describing
the advertised capacity of the tape.  If, because of IRGs or 
bad media, the actual capacity of some of the tapes is less than
the advertised capacity, it's not a catastrophe because dump handles
the EOT correctly.

So, to answer the questions:

    For $8K: some sites may choose to put more than one dump on
      a single 8mm tape.  This makes a lot of sense for dailies
      and even weeklies.  As a result, any given dump file may
      not start at the beginning of the tape.

    For $64K: some versions of dump do deal with end of tape.
      I think they all should.

--
Brian Hackworth
Data General Corporation                hackworth at dg-rtp.dg.com
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