One of my libraries is getting close to maxing out its storage.  Its a
Breece Hill Q47 with 3 DLT4000 drives.  I'd like to replace the drives with
4 DLT8000 drives.  So far I've been hearing it should all be backward
compatible but mostly thats just from the sales people.  Some of the people
around here think a DLT4000 tape should be readable in 7000 or 8000 drive.
Is this correct?

If it is correct then is it possible to just replace the drives in the
library redefine them to AIX and ADSM and continue on?  In other words will
ADSM even notice?  We are running ADSM 3.1.2 L40 on an RS/6000.

I am thinking it should be fine but I am mainly wondering how new data gets
written back out to media?  Will new data being written to tape need to
write on a scratch volume or can it just be written on a filling volume?  Or
is all of this too much of a hassle and I should just buy a new library and
migrate the data over to it?  Is there any sort of procedure defined
someplace I could use?

Thanks for any input
Jack