User's Guide

Quantum Scalar Intelligent Libraries SCSI Reference Guide Guide 9
Fibre Channel Interface Support
The library Fibre Channel ports can be N_Ports for point-to-point topologies or NL_Ports for arbitrated loop
topologies. Only Class 3 service is supported. Private arbitrated loops are supported if the library is not
attached to a Fibre Channel fabric, and public arbitrated loops are supported if the library is attached to a
Fibre Channel fabric.
Logical Libraries
The underlying physical library is not exposed externally to applications. Rather, logical representations of
Media Changers are created, and these are presented instead. Through this method the physical library can
be partitioned and concurrently shared in a heterogeneous environment. Storage and Data Transfer
elements cannot be shared across logical libraries; they can only be assigned to one logical library at a time.
The Medium Transport element (the robotic mechanism) is shared across all logical libraries, and as a result
there may be some delays encountered as each logical library waits its turn for this shared resource.
Depending on library model, Import/Export elements can also be shared across logical libraries. This is
further discussed in Mailbox Behavior
. All other aspects of the logical Media Changers are identical to an
independent physical Media Changer.
Mailbox Behavior
The following characteristics affect Import/Export elements:
• The Import/Export elements are contained in removable magazines. When the magazines are
removed, the elements are still counted in the number of Import/Export elements and will have
element descriptors returned for them in response to a READ ELEMENT STATUS command. Their
element status will indicate that they are not accessible, and will also report an exception with an
ASC/ASCQ of 3B/12.
• Some libraries are configured with multiple physical mailboxes, each containing their own set of
magazines. Whenever a mailbox is opened, the status for the elements it contains will indicate that
they are not accessible until the mailbox is closed again.
• The mailbox magazine(s) can be assigned to and shared by different logical libraries. The Import/
Export elements they contain are then used on a “first come, first served” basis. When shared
Import/Export elements are in use by one logical library, element status for those elements will
indicate that they are empty, but not accessible for all other logical libraries that share them. The
presence of media and associated volume tag information will only be available to the logical library
using the elements at that time. When media is removed from the shared elements, they become
available for use by the next logical library requesting them, and their element status indicates that
they are accessible.
These characteristics require applications to process the complete element status returned in the element
descriptors (including accessibility and exception conditions) to achieve optimum usage of the Import/
Export elements. Reliance on only full or empty element status may result in failed operations (e.g., an
Export). This might be due to not locating a usable Import/Export element when several may actually be
available, if the search had only taken into account full status rather than accessibility.