[Info-vax] Copying VMS SaveSet Under Windows

[Johnny Billquist]

On 2010-11-22 02:00, glen herrmannsfeldt wrote:
> Bob Eager<rde42 at spamcop.net>  wrote:
> (snip on unix and blocks
>
>> Not quite. It is able to differentiate between tape blocks, and between
>> data and tape marks. That is all that is needed to clone a real tape into
>> a SIMH 'tape file'.
>
>> If you issue a sufficiently large read (>  max block size expected) on a
>> tape device in UNIX, it'll return a buffer with the contents of the next
>> block, and it'll tell you how many bytes there are in that buffer. Or,
>> it'll return a status value saying that it encountered a tape mark.
>
> Even more, if you use dd with the bs option, for a tape to tape
> copy, it will preserve the block size.  That is different than
> the ibs and obs options, which reblock the data to the specified
> obs block size.
>
> With bs=(large value), dd reads one block, writes one block,
> reads the next, writes that, etc.

It will not "preserve" the blocksize. You will just not loose any data, 
but the block size information is lost.

If you want to preserve the blocksize, so that you can recreate the tape 
at a later date, you need to write your own program under Unix.

Feel free to ping me if you want. I have written such a beast (as I'm 
sure many others have), and I've published it in the past, and can sent 
it to anyone who needs it.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol