tar.c & blocksize

[Barry Shein]

>From: lm at geowhiz.UUCP (Larry McVoy)
>Subject: tar.c & blocksize
>...
>My question is this:  is it asking for trouble to play with the NBLOCK 
>definition in tar.c?  Some people here have raised the question of 
>compatability, ie. what about other sites, what if they don't have source
>and/or can't get a hacked version of tar?  On the other hand, it seems that
>the savings in time are great enough to warrent a change.
>
>If you have an opinion on this, I'd like to here it.
>
>-Larry McVoy		[ARPA]	mcvoy at wisc-rsch.arpa
>			[UUCP]  ...!uwvax!geowhiz!lm

As discussed before, there is already a problem. The default blocksize
for 4.2bsd tar creates a tape that (as far as I can tell) can not
be *physically* read by the tape drive on my SYSV/3B5 due to controller
limitations. Making it larger, however, makes it no worse :-)

I would suggest you warn your users or, better, not make it the
default. You should probably warn your users anyhow, I suggest
going no larger than 5 (tar cb 5 ...) if you really don't know
who is going to read this tape. As an aside, I still swear I blew
the circuit breakers twice on my TU78 by specifying a block size
of one at 6250. (Data General also makes it tricky to read tar
tapes with physical blocks larger than 8192 though it can be done.)

	-Barry Shein, Boston University