ACL 4/52 Software Interface Guide
Document 6211225-03
Version 3.0
System Performance
2-15
System Performance
Key Performance Items
The actuator move times are the key performance items. The internal
software attempts to maximize the library’s performance by allowing
multiple actuators to move simultaneously. For example, the vertical
and horizontal axes are moved to the appropriate position at the same
time when moving toward a storage element, i.e., diagonally. Also, the
extension and gripper actuators are moved to a ready position after
the completion of a move to prepare for the next move.
The host can increase performance by minimizing the distance of the
actuator moves. It can do this by using the time when the tape drives
are busy (or when no commands are being issued) to sort the storage
elements to better suit the application.
Typical Application Enhancements
The host should check for any attention or error conditions that the
tape library may have buffered by issuing Request Sense Commands
until no conditions exist.
The SCSI interface allows the host to enable the “disconnect from bus”
option. This allows the target to disconnect from the bus while
processing a command from the host application and reconnect when
the command is complete. Disconnecting allows access to the drives or
other logical units while the command is being performed.
The internal software does not support command queueing. It is up to
the host application to queue commands to the unit. It may also be
advantageous for the application to group queued commands to
require the least amount of actuator motion.
The Position To Element command allows the application to move the
robotics to a more advantageous position while the tape drives are
busy. For example, if a DLT™ is about to be ejected from the drive, the
robotics can be positioned in front of a drive to pick up the DLT™
when ejected. (The host should verify that a tape is present before
attempting a “pick” operation. If the tape drive is not unloaded, the
error “MEDIUM NOT PRESENT” {SK=5 ASC=3A ASCQ=00} is
returned and the host should attempt to retry.)