On Wed, 19 Dec 90 19:30:47, I sent a query out about copying 1/4"
SunOS distributions (given licensed right to do so). I've gotten
over 40 responses - I thank everyone who took the time to reply.
My conclusions follow:
- There is no blocking factor on cartridge tape in the sense that
1/2" magtapes have blocking factors. Cartridge tapes use fixed
512 byte physical blocksizes, period.
- Assuming a sufficiently large file on the tape, no matter what
request size you use on a READ, you will get that many bytes
back. A tape written with 10 512 byte "blocks" can be read via
5 1024 byte reads - the data is the same either way.
- Specifying blocksizes does have some effect on the speed of the
I/O operations, presumably due to the way the Operating system
drivers, the SCSI bus and the tape controllers work.
- 126b (b=512 bytes) is one "recommended" blocksize, one rumor was
that it was because of some limit on the SCSI bus. I've also
seen 200b as another "recommendation", but there was a recent
posting to sun spots where the sender had experimented with large
blocksizes (1000b) and found them faster. I too have been using
huge blocksizes with success now. At any rate, the blocksizes
are pertinent due to system buffering of some sort, not because
of the physical layout of the tape.
- There appear to be some software bugs under SunOS 4.0(.x?)
somewhere in the cartridge tape code. I've seen code written to
reposition the tape after each file was written via rewinding
and spacing forward again. For some reason the tape being
written loses its position. I'd like to hear from anyone that
can verify this. I just found I had to do this under 4.1, so
perhaps its more than a mere software bug. Only seems necessary
- My odd problem where I have to specify a blocksize of 1b to read
the first file on a Sun 4.1.1 distribution tape to avoid getting
an "i/o error" seems to be dependent on the operating system and
tape drives I use. People at other sites read the same file
with a large blocksize just fine, as do I on other 4.1 systems.
I suspect something odd about our installation, or perhaps
another 4.0.3 bug?
- A recommended reading: "Tutorial on 1/4" Tapes" from Sun, their
part number 800-1315-02.
How do people copy distribution tapes?
- MANY people recommended "copytape", a public domain tape copier
written by David Hayes of the US Army AI Center. It is available
from the uunet comp.sources.unix archives (volume 10).
- Several people mentioned "tcopy", which comes with SunOS 4.0 and
- Several people use the Sun Consulting Services "special" called
"tputil". Tputil works well, and will also verify tapes.
- Many people do what I do: use scripts that do multiple dd's.
Well, that's enough. I understand from one responder that someone in
Sun Consulting is working on a program/script that will take a
distribution CD and create bootable tapes from it. That sounds like a
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