...
>We are soon going to be upgrading our 3590 B1A drives to the H1A models so
>that we can squeeze loads more on the tapes and free up slots in our
>soon-to-be-filled library.
>
>Now, as far as I am aware, this is a relatively simple operation. Am I
>right in thinking that all that needs to be done after the drives have been
>upgraded is to mark all tapes that are presently in the on-site Tapepool
>(in the library) as read only. After this, only scratch tapes will be used
>and I will be free to start running some movedata commands to start
>consolidating tapes (using the new higher compression).
...

3590H upgrading is fully covered in the server README file.