We have 3 STK 3490-compatible tape drives in an automated library.
We very commonly have more than one tape in "filling" status.

One way this can happen is if your disk storage pool fills up during
backups.

If a client is backing up to the disk pool and runs out of space, ADSM
mounts a tape and the client starts writing directly to the tape.  I
have had cases where a client was dumping data to the pool so fast that
disk migration started to the available "filling" tape, but migration
did not clear the pool fast enough and a second tape got mounted for the
client backup.
Result, two tapes in "filling" status.

The same thing can happen if a reclaim is writing to an output tape at
the time disk migration starts - a second output tape gets mounted for
the disk migration.

You could prevent both situations with more careful scheduling and
carefully controlling the size of the disk pool, but I haven't found it
to be a problem.  We move a lot of data every day, so the "filling"
tapes all get used and filled up within a day or two.

>----------
>From:  Hilton Tina[SMTP:HiltonT AT is1.indy.tce DOT com]
>Sent:  Thursday, March 27, 1997 7:07 AM
>To:    ADSM-L AT VM.MARIST DOT EDU
>Subject:       Re: why two tape are filling
>
>I've noticed this sort of thing too.  We have 2 tape drives, so I would
>expect only 2 tapes to be in filling status yet we have 7.  All of them are
>read/write.
>
>On another note, I had a weird experience with reclamation yesterday.  Two
>tapes were processed by reclamation.  The contents of the first tape
>(status=full) was moved to a second tape.  The second tape then was
>reclaimed (it's status was still filling) and its contents moved to a third.
> Why on earth would ADSM move the data from tape 1 to tape 2, only to move
>it all again to tape 3?  I think it goes back to no logic in selecting the
>order of the tapes to be reclaimed.  If ADSM had looked at all the tapes
>that would be processed, it wouldn't have handled it this way.   I hope I
>never get to the point where I have several tapes in filling status that
>also are eligible for reclamation.  It would take forever to move the data
>from tape to tape to tape ...
>
>Tina Hilton
>Thomson Consumer Electronics
> ----------
>From: Julie Xu
>To: ADSM-L AT VM.MARIST DOT EDU
>Subject: why two tape are filling
>Date: Wednesday, March 26, 1997 6:34PM
>
>
>Normaly, we have only one tape to be filled at a time. But today, I
>found there are two tapes' status is filling. what is the cause?
>
>We have adsm server on sp2/aix 3.4 and a 3590 drive. the message is:
>adsm> q vol
>B010    BACKUPTAPE   3590TAPE  9,169.4 77.5    Full
>B011    BACKUPTAPE   3590TAPE  9,072.7 81.8    Full
>B012    BACKUPTAPE   3590TAPE 10,000.0 22.9    Filling
>B013    BACKUPTAPE   3590TAPE 10,000.0 16.4    Filling
>B014    BACKUPTAPE   3590TAPE      0.0  0.0    Empty
>
>Any comments will be appreciated
>
>Thanks in advance
>
>Julie Xu
>email: j.xu AT uws.edu DOT au
>