Random and Sequential Logical Library modes

A Logical Library can be configured in one of two modes: Random and Sequential.

Random Mode

Random Mode is intended to be used by host applications that support SCSI media changer devices. Random Mode is the default.

In Random mode,
  • The host application chooses the cartridges that are moved to the drive.
  • I/O slots provide the flexibility for the user to add and remove cartridges and the host application is automatically notified of these changes.
  • Multiple drives can be assigned to provide parallel processing data operations and redundancy in case of failure.

Sequential Mode

Sequential Mode is intended to be used by host applications that aren’t supporting SCSI media changer devices but need to get another cartridge loaded if the current cartridge is full.

In Sequential Mode,
  • The library predefines the sequential order that the cartridges are moved to the drive.
  • I/O slots are hidden as they aren’t assignable to a logical library with sequential mode enabled.
  • Only one drive can be assigned to a logical library with sequential mode enabled.
  • There’s no control path drive and no media changer device is configured to the host server.
Options to consider when Sequential Mode is chosen:
  • Basic Function - To initiate use of cartridges, the user issues a Move Cartridge command to the drive through the Management GUI. After the load, the host application can begin data I/O activity. When the host application unloads the drive, the library moves the next cartridge into the drive. This behavior is implicit, unless otherwise defined by selection of another option.
  • Loop Option - If a move sequence ends because no more cartridges are available in the current logical library, the sequence starts again by loading the first cartridge of the logical library. This option can be chosen with or without the Autoload function.
  • Autoload Option - If enabled, the library loads the first cartridge of the logical library to the Sequential Mode tape drive during library startup after inventory scan is finished. This option changes the implicit behavior of the Basic function. This option can be chosen with or without the Loop option.

If storage slots are configured to I/O slots after assignment to a Sequential Mode logical library, they are still considered valid available slots and are used for movements. This option stays until you run the expert wizard again, and then these I/O slots no longer appear in the list of available slots. Finishing the expert wizard then sets the new slot assignment and these I/O slots can no longer be used for movements.

To enable sequential mode, click the Enable Sequential Mode check box in the Manage Logical Library (Basic Mode) Wizard or Manage Logical Library (Expert Mode) Wizard.