1. Administrator's Guide
  2. Logical Library Support
  3. About Logical Libraries

About Logical Libraries

A portion of the ACSLS physical library configuration can be presented to SCSI clients as a logical library that can behave as a target device on the SAN. A logical library, in reality, is a defined parcel of a physical library with specific user-assigned resources including tape drives and volumes. Logical libraries are exposed to client application software through a SCSI (fibre-attached) interface.

A fibre channel HBA port typically operates in initiator mode, and can issue SCSI requests to a remote target device such as a disk drive, tape drive, or media changer device. In order to use logical libraries, you must configure one or more fibre ports to operate in target mode instead.

You can select one or more FC ports for target mode operation, or set target mode ports back to initiator mode, when running the install.sh or the getHba.sh utilities. A reboot is required for any change to take effect.

A logical library can be created using any eligible physical library as the backing ACS. The backing ACS identifies the physical library from which the logical library is created. The backing ACS:

  • Must be configured to the ACSLS library server, but it need not be online in order to create a logical library.

  • Can be an entire physical ACS, or it can be a physical partition of an ACS if the library itself supports physical partitioning.

To create, manage, or delete logical libraries, you can use either the ACSLS Graphical User Interface (GUI) or the lib_cmd Command Line Interface (CLI).

Benefits

Logical libraries enable you to do the following:

  • Partition physical libraries into logical libraries.

    Logical libraries can be managed and used by client applications as if they were separate libraries.

    ACSLS provides a flexible partitioning mechanism that is not tied to specific physical storage locations. A logical library is defined in terms of volumes and drives, and ACSLS presents these to the client using logical locations. The logical library is not limited by any physical divisions within an ACS, such as panel or rail boundaries.

    Logical libraries also protect clients from potentially disruptive changes. When ACSLS chooses a new physical home cell for a volume, keeping it close to a compatible drive, or when an existing logical library is expanded, the client application is not impacted.

  • Report the entire 8-character barcode as the volser.

    When creating your logical library, you can specify the volume label format for clients: 6-character, 8-character-prefix, 8-character-suffix, or all. The 8-character barcodes include media domain, and type after or before the volser.

    Note:

    Volume labels longer than 6 characters are not accessible to ACSAPI clients.

  • Manage client access to drives and volumes.

    Drives and volumes that are assigned to a logical library are accessible only to the client that is using the library, and are not visible to other FC or ACSAPI clients. However, the ACSLS GUI and cmd_proc are able to see them since these interfaces operate in system administrator capacity.

  • Provide multiple initiator support.

    A logical library can be made accessible to multiple clients (specifically, to multiple initiator ports). The purpose is to support redundancy on the client side, not to allow simultaneous operation of a logical library by multiple clients. Only one client system should operate a logical library at a given time.

    Allowing multiple initiators means that a single client system can access their assigned logical library over multiple FC HBAs or ports. If the client environment supports a fail-over capability, the logical library is immediately accessible to the new active client system.

    Any Unit Attention or Check Condition raised for a logical library is presented on each connection that has been configured.

Limitations

Logical libraries:

  • Are only accessible to clients using the ACSLS SCSI Media Changer Client Interface. They are not available to clients that use the legacy ACSAPI.

  • Cannot span more than one physical ACS (or physical partition).

  • Cannot reserve specific storage cells in the physical ACS. Combining logical and physical partitioning would be a way to accomplish a similar result.

  • Target mode FC ports may no longer be included in the output from certain Solaris commands, such as fcinfo.