Gerhard,   Here's the answers to your questions.

1. I think the checkin libvolume would take some time if I specify
checklabel=barcode as  indicated in the README. Is it a good idea to
specify  checklabel=no? I'm quite sure that all necessary volumes are in
the silo. How long would the checkin take in this case?
>>>  "Checklabel=no" would require you to checkin each volume one at a
time.  To use the search=yes option for checkin, you must specify either
checkl=yes or checkl=barcode.  The barcode is much faster than reading
the internal label.

2. Is there any danger that the checkin command causes loss of data which
is on the volume? What happens if a volume with data on it is checked in as
scratch?
>>> The checkin process checks for this condition.  If you specify
status=scratch and a there is a storagepool volume by this name, it will
fail the checkin.

3. What is the difference between devtype CARTRIDGE and ECARTRIDGE? I have
STK 4490 and have used the so far as CARTRIDGE without problems. Should I
change the devtypes?
>>> There's a big difference.  ADSM even lays the data out differently.
You cannot change devtypes from cart to ecart, anyway.
There was a special case allowed (for  migration from Enhanced ADSM
only) for changing it to Generic, but I don't recommend this.  You have to stay
with Cart.

>>> Are you going from ESCON to SCSI?  If you cannot
configure the SCSI connection to these drives with the Atape device driver,
you'll need to stay with ESCON, because you cannot change the devtypes.
Lucky for you, the Atape driver supports both ESCON and SCSI using the
devtype of Cart, but be aware that Atape does not officially support 4490's.
(Actually, 4490's aren't officially supported by mtdd either, but a lot of
people do use these IBM drivers for STK drives)

Craig Bell