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From: anders@perdix.lu.se (Anders Ardo )
Newsgroups: comp.unix.questions
Subject: backup, ts11 block size, megatape
Message-ID: <197@perdix.lu.se>
Date: Thu, 25-Jun-87 18:58:04 EDT
Article-I.D.: perdix.197
Posted: Thu Jun 25 18:58:04 1987
Date-Received: Tue, 30-Jun-87 05:19:41 EDT
Organization: Computer Engineering, University of Lund, Sweden
Lines: 31

I have some trouble getting performance out of a Megatape backup
magtape. I have a uVAX running Ultrix 1.1. The Megatape is driven by
the ts11 driver.
Using only the dump command it takes ~ 2.5 hours to fill one tape with
340 MB of data. The tape should nominally hold 500MB. I am told that
the ts11 driver uses 8k blocks which should give this amount of tape
utilization.
If I could increase the blocksize to 32768 (maximum for ts11) the tape
utilization would increase to 438 MB and the time to write the tape
should go dowm.
I tried to do this using the method suggested here earlier with the
following command:
dump 0nf ... | dd obs=32768 conv=block of=/dev/rmt9
This method works fine with the TK50 drive on the same uVAX giving
speed ups of 2-4. BUT for the Megatape - ts11 I actually get a
slowdown from 2.5 hours to 11.5 hours?    WHY??
Can I do something else to achive this blocking of 32768 for The
Megatape or are theer anything else I can do to speed up backups?

I have also heard rumors about backup units based on videotapes with
capacities of 1 to 2 GigaBytes. Anyone have some more information or
even  experience with these kinds of backup units?

Thanks for any hints or suggestions.
      Anders

   Anders Ardo                         Tel:    int+46 46 107522
   Dept. of Computer Engineering       Telex:  33533 LUNIVER S
   University of Lund
   P.O. Box 118                        UUCP:   anders@perdix.lu.se
   S-221 00  Lund, Sweden              BITNET: ddtnet@seldc51