Trying to detach a system board	with DR (Dynamic Reconfiguration) CLI
with a StorageTek library silo that uses dlt tapes.
Error occurs when trying to complete the detach;

"DR Error: Error detaching board (st28): ioctl failed....I/O error"

Ran; 

modinfo | grep -i tape

to get the "st" module id number "94"

tried a "modunload -i 94" 
to unload the st module, it says;

"can't unload the module: Device busy"

which is why the detach cannot complete.

The following entry has been copied into the /etc/system file 
(from Bug Id: 4042415)

set dr:detach_safe_list1="st"

but did not help.

To complete the detach:

1) Load a tape into the drive.

2) Run  "mt -f /dev/rmt/0 offline"  (if it's a jukebox do it for all devices).

3) Run "modinfo | grep -i tape" (get the id#).

4) Run "modunload -i id#"

5) Complete the detach in the dr window.