🚀 go-pugleaf

In article <7527@lindy.Stanford.EDU> CN.RNA@forsythe.stanford.edu (Richard Anderson) writes:
>
>I have a question regarding the "dump" command.  The AOS4.3
>System Administration manual (which I have found very useful
>and clearly written) has a chapter on Backup & Restore, in which
>a refererence is made to the 6157 streaming tape drive, followed
>by an example of the dump command:
>
>      dump 0suf 2600 /dev/st0 /dev/rhd0a
>
>They use a value of 2600 ft for the length of the tape and accept
>the default density of 1600.  However, the DC6150 tapes I use on my
>6157-002 drive are 600 feet long and have a density(?) of 12,500
>ftpi.

Tape drives are not my specialty but I will give this a try.   A more
practical measure of the density is 12K bytes / foot.  The type 2
drives write at a higher density, but it will be easier for users of
dump to pretend the type 2 drives make their tapes twice as long.

The example's use of 2600 is not appropriate for the streaming device.
Dump's default length for a streaming tape in the BSD Tahoe release is
1700 feet.  This is 450 feet times 4 tracks (presumably appropriate for
Tahoe hardware).  In IBM 4.3, the default length is 4000 feet (450 x 9). 
For a 600-foot tape with a type 1 (original model) drive, use 5400
(or 5300 if you are as paranoid as I am).  If you have a type 2 (double
density drive), you can specify 10000.  At 12K bytes per foot, you can
get 60 megabytes on a 600 foot tape (120 megabytes using a type 2
drive).

This posting is based on my personal experience and examination of the
dump source code.  It does not represent the official postion of IBM.
Any errors are my own responsibility.

-- 
charlie slater
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