Very Computer

I'm not really sure to post this, I hope it's relevant.
The NetBSD-specific part is at the bottom.

My problem is that I don't understand blocking factors.

I know how to use tar to increase it; no big whoop.  But how are blocks
delimited on the tape?  With an escape code, file header, or out of band
info?

How come when I gzcat and redirect to the raw tape device, Solaris tar
complains "blocksize=2"?  How does it know, and how can I set it?  Do I
have to pipe thru cpio or dd or something?
--

WARNING: Unsolicited commercial e-mail: $500 per message
US Code, Title 47 Section 227 (http://www.law.cornell.edu/uscode/47/227.html)
This message may not be redistributed on the Microsoft Network.

: I'm not really sure to post this, I hope it's relevant.
: The NetBSD-specific part is at the bottom.

: My problem is that I don't understand blocking factors.

: I know how to use tar to increase it; no big whoop.  But how are blocks
: delimited on the tape?  With an escape code, file header, or out of band
: info?

: How come when I gzcat and redirect to the raw tape device, Solaris tar
: complains "blocksize=2"?  How does it know, and how can I set it?  Do I
: have to pipe thru cpio or dd or something?
: --

: WARNING: Unsolicited commercial e-mail: $500 per message
: US Code, Title 47 Section 227 (http://www.law.cornell.edu/uscode/47/227.html)
: This message may not be redistributed on the Microsoft Network.

I would like to expand on this question.  Many of the new streamer tapes
are "pre-formatted" (QIC-80, QIC-WIDE, and others).  Can anyone provide
info on the block sizes for these tapes?

Clayton Valley

I am not certain how things work on many of the new tape drives, but I can tell
you how things used to work on 9 track reel-to-reel tapes (and 7 track if you
remember those).  But I suspect that the concepts have not changed much.

What is generally called a "block" when talking about tape writing software is
called a "record" when dealing with the tape controller.  This is the smallest
unit that can be read or written.  The controller writes "records" to the tape,
separated by Inter-Record Gaps.  It can also write "tape marks", which are often
used to delimit files.  Two successive tape marks without intervening records
indicates the end-of-tape.

It is interesting to note that the Inter-Record Gaps were physically rather
large, approximately 3/4 of an inch.   This meant that the record (block) size
had a rather profound effect on tape capacity.  On a 6250 bpi drive, 80 byte
records would occupy 80/6250 = 0.128 inches.  With a 3/4 inch gap between each
record, this meant that the tape held 1.7% data and 98.3% Inter-Record Gap.

-- John McGrath