[Info-vax] Copying VMS SaveSet Under Windows

[glen herrmannsfeldt]

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.

-- glen