Ultrix dump to TK50 not using entire tape?

[Joseph S. D. Yao]

In article <257 at cirl.UUCP> das at cirl.UUCP (Dave Steffens) writes:
>We are running Ultrix version 1.1 on a uVAX II with TK50 cartridge tape drive.
>When dumping our main filesystem to TK50 tape, we noticed that each cartridge
>appears to hold only about 40Mb instead of its rated capacity of 95Mb.
>What's going on here?

The default for dump is to assume size 2300', 1600 bpi, blocking of
10 (*1024), 9-track magnetic tape.  This gives us 27600" of tape,
with 10240 bytes/tape block, or 6.4" + 0.7" IRG (InterRecord Gap).
27600/7.1 ~= 3887.324 10K blocks, or ~38.87 Mb.  Several ways out
include (documented) key B to tell it how many K long the tape
really is; or (undocumented) key 'c', which sets all the parameters
correctly for a cartridge.  (Another undocumented key is 'b', to
change the blocking factor.  Use 'c'.)  Let me know whether 'c' also
increases your speed/efficiency.

[The above formulae assume 1600 bpi 9t => 1 byte/linear bit space.]

This is under Ultrix 1.1 on a VAX; I'm assuming similar code for
your uVAX II.  The kernel code is the same.
-- 

	Joe Yao		hadron!jsdy at seismo.{CSS.GOV,ARPA,UUCP}