[Info-vax] Copying VMS SaveSet Under Windows

[Johnny Billquist]

On 2010-11-29 21:55, glen herrmannsfeldt wrote:
> Johnny Billquist<bqt at softjar.se>  wrote:
> (snip, I wrote)
>
>>> 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.
>
> When dd runs with the bs= option, it reads a block (up to blocksize),
> then writes that block (of whatever size) to tape.  Repeat until EOF.
> The blocks written have the same size as the blocks read, unless one
> is bigger than bs.  If you specify both ibs= and obs=, then the
> data is reblocked to the obs size, and block information is lost.

Hmm. I must admit that I've never tried dd directly between two tapes...
But that's a neat trick. But you need two tape drives to do it.

>> 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.
>
> If you dd to disk, then the block information is lost.  That comment
> was for tape to tape dd.

Ok. Gotcha.

	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