🚀 go-pugleaf

Patrick Robinson writes
> intend to use dump/restore forever, I'd sure like to understand how to make
> it work.
> 
> Here's the problem:  I'm having trouble understanding the man page for the
> dump command.  Down under the notes for 'DUMPING TO EXABYTE TAPE', there's
> an explanation about setting the s paramter, which specifies tape size in
> feet.  They make the claim that a 1.985 Gb Exabyte tape (120 minute 8mm)
> would be equivalent to 1,332,183 feet of 1600 bpi reel-to-reel tape.  I
> don't see where they get that number.  According to my calculations:
> 
> 1.985 Gb   1,073,741,824 bytes   8 bits      1 in      1 ft  ~
>          * ------------------- * ------ * ---------- * ----- = 888,074 ft
>                 1 Gb             1 byte   1,600 bits   12 in
> 
> rather than 1,332,183 ft.

Two things:
	1.	The man page is wrong.  A single tape with the stated capacity
is actually about 110,000 feet.
	2.	1600 bpi is for *each* track of the 9 track tape.  Normally one  
track was for parity, so it worked out to 1600 bytes/inch of tape.
	This confusion above makes your answer correct.  (eliminate the  
8bits/byte conviersion)

	The only reason you care at all about this is that dump multiplies it's  
default bpi x 12 x length in feet to get the amount of stuff that will fit on  
the tape.  This is used to figure out when to ask the operator to change tapes.

	So you could do this by either telling dump that your tape is only 30  
meters long, and it's density is a zillion bits per inch, or by letting it  
assume a 9 track tape, that's rather long.