Dumping to an exabyte tape drive

[Frank P. Bresz]

In article <32608 at sparkyfs.istc.sri.com> zwicky at sparkyfs.istc.sri.com (Elizabeth Zwicky) writes:
>In article <877 at iiasa.UUCP> wnp at iiasa.UUCP (wolf paul) writes:
>>These figures seem quite inconsisten. Which is correct?
>>Would someone at SUN care to comment, ideally the person who wrote
>>their drivers?

>>Jim Tibbs specifies a density of 43000 bpi and a length of 12000 feet
>>Derick Linegar specifies       4100000 bpi and a length of  5190 feet
>>Frank Bresz specifies density of 54000 bpi and a length of  6000 feet

>OK, so I don't work for Sun and I didn't write their drivers, but
>since this actually has nothing to do with Sun's generic SCSI driver,
>that's probably just as well.

>Basically, dump takes these numbers, multiplies the number of feet by
>120 to get tenths of inches, munges that some to compensate for
>interrecord gaps, and multiplies the result by the bytes-per-tenth of
>inch to get the number of bytes that will fit on the tape. This works
>fine for cartridge tapes, and 1600 bpi half-inch. Beyond that, life
>gets bad, for several reasons.

[...] Stuff deleted

>So part of the trouble here is that telling dump the truth won't work,
>several times over; dump can't cope with the truth, and even if it
>could, its idea of an interrecord gap is wildly off and so it would
>get wrong how many could fit. So why do people use different lies?
>Different blocking factors; different device drivers; different
>versions of dump (OSU's fast dump redoes the interrecord gap
>calculations and bumps the shorts to ints and the ints to longs,
>bypassing problems 2) and 3)); different guesses, for that matter. As
>long as your largest filesystem is smaller than an exabyte, and also
>small enough that dump thinks it will fit, it really doesn't matter.
>If it won't fit, play with the parameters...

>	Elizabeth Zwicky

I was stating what I used because I found it didn't give me great results.
These numbers were listed in my ARTECON manual I received with the tape
drive and also in the SunOS4.1 man pages (See end of post, I hope a verbatim
quote from the manual doesn't get me in trouble).  

I have since switched to Derick's set of numbers but the following results
ensued.

  DUMP: estimated 8802 blocks (4.30MB) on 0.00 tape(s).
  DUMP: estimated 22876 blocks (11.17MB) on 0.01 tape(s).
  DUMP: estimated 59102 blocks (28.86MB) on 0.02 tape(s).
  DUMP: estimated 143484 blocks (70.06MB) on 0.04 tape(s).
  DUMP: estimated 179616 blocks (87.70MB) on 0.05 tape(s).
  DUMP: estimated 213900 blocks (104.44MB) on 0.06 tape(s).
  DUMP: estimated 395718 blocks (193.22MB) on 0.12 tape(s).
  DUMP: estimated 545608 blocks (266.41MB) on 0.17 tape(s).
  DUMP: estimated 730660 blocks (356.77MB) on 0.22 tape(s).
  DUMP: estimated 806998 blocks (394.04MB) on 0.24 tape(s).
  DUMP: estimated 894876 blocks (436.95MB) on 0.27 tape(s).

Hand computed totals

  DUMP: estimated 4001640 blocks (1953.92MB) on 1.20 tape(s).

So while it is closer there is still a posibility of dump stopping before
the tape is truly full.  As you can tell from this listing I am getting
close. I guess I can just bump up the feet a touch more to see what
happens.  As per Elizabeth I shall just keep lying until dump finally hears
the lie it wants to hear.

P.S. This tape also has a complete index at the head and tail end of the
tape, so there is even a touch more data there.

SunOS4.1 Man Page on 'dump' says:

     d bpi
          Tape density.  The density of the  tape,  expressed  in
          BPI,  is taken from bpi. This is used to keep a running
          tab on the amount of tape used per reel.  Default  den-
          sities are:

               1/2" tape                1600 BPI
               1/4" cartridge           1000 BPI
               2.3-Gbyte 8mm tape       54,000 BPI

     s size
          Specify the size of the volume being  dumped  to.  When
          the  specified  size  is reached, dump waits for you to
          change the volume.  dump interprets the specified  size
          as  the length in feet for tapes, and cartridges and as
          the number of 1024 byte blocks for diskettes.  The fol-
          lowing are defaults:

               1/2" tape                2300 feet
               60-Mbyte 1/4" cartridge  425 feet
               150-Mbyte 1/4" cartridge 700 feet
               2.3-Gbyte 8mm            6000 feet
               diskette                 1422 blocks
--
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