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StorageTek SL150 Modular Tape Library Systems Assurance Guide 22579-04 |
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# B Partitioning Overview

The SL150 library can be partitioned into two distinct sections.

Briefly stated, this means that instead of one library—with all its cartridge slots, tape drives, and mailslots—being a single entity, the library and these components can now be divided into two sections or partitions. Each partition can be accessed by one host or multiple hosts.

## Partitioning—General

Partitioning has terms associated with it that you and your customer must understand to effectively use the feature. In certain cases, these terms redefine some concepts that are familiar with users of the traditional, non-partitioned library configuration.

A "partition" is defined as the process of dividing portions of a library into discrete sections. The partitioning feature offers great flexibility for users.

Enabling the library to be partitioned requires some important considerations:

- Each partition designates tape drives solely to its partition, the other partition cannot use these tape drives.

- Partition users must anticipate how much storage area is needed for their resident tape volumes and the amount of free slots required. Once storage needs are defined for the partitions within the library, sufficient modules need to be present within the library to accommodate this need.

The SCSI element numbering within partitioned libraries is continuous for each partition.

## Partitioning—Feature

The SL150 library supports two partitions.

Important: You must enable the partitioning feature through the administrator role within the Settings Screen under the Partitions tab. Online help within the library explains the partitioning configuration presented when partitions are enabled. Only the administrator can enable or disable the partitioning feature.

The customer has the choice of a non-partitioned library or a partitioned library with 2 partitions. When a partitioned library is desired, the library uses the following simple method for dividing the resources in 2 partitions:

- Storage Slots

  Partition 1 owns all storage slots on the left side of the library.

  Partition 2 owns all storage slots on the right side of the library.

- Tape Drives

  Partition 1 owns the top tape drive in the base module and the top tape drive in each additional expansion module.

  Partition 2 owns the bottom tape drive in the base module and the bottom drive in additional expansion module.

- Mailslot Elements

  The mailslot elements are shared by both partitions.

Using Figure B-1 as an example, partition one owns the left side of the base and the expansion modules, SCSI element numbering begins at the first available slot in Module 1 and continues through the expansion module slots. The first drive in the top module will begin the element numbering for partition 1 and continue to each top drive slot in all expansion modules that are installed.

The library will discover the current number of modules at each boot up. If you shut down the library and then boot up, the partitions will redefine to the current number of modules.

After ENABLING partitioning, the library sets the bridged drive for each partition:

- The bridged drive for partition 1 is the top drive in Module 1. Partition 1 owns all tape drives in the top slot of each module.

- The bridged drive for partition 2 is the bottom drive in Module 1. Partition 2 owns all tape drives in the bottom slot of each module.

### Partitioning—Access Control

All hosts that issue commands to a bridged HP LTO-5 or LTO-6 drive may also send commands to the library partition. Commands are processed by the partition in which the bridged drive resides. The host sends commands to the drive on LUN 0 and to the library on LUN 1.

Figure B-1 Partitioned SL150 Modular Tape Library

Illustration Legend:

1 - Module 1 (Base)

2 - Partition 1

3 - Partition 2

4 - Robot

5 - Power supplies

6 - Tape drives

7 - Mailslots

8 - Left magazine front

9 - Right magazine front

10 - Module 10 (Expansion)

11 - Partition 1 resource

12 - Partition 2 resource

13 - Shared resource

14 - Reserved slots (configurable, shared resource)

### Partitioning—Shared Mailslot Behavior

When the library is partitioned, the mailslots are shared between the two partitions. When a partition needs access to the mailslots, the operator must use the ASSIGN action in the user interface to assign the partition to the mailslots before initiating an import or export operation. Refer to the SL150 Users Guide for help.

A Partition-Mailslot assignment gives a partition exclusive ownership of the shared mailslot. This ensures that cartridges are always entered into the correct partition and prevents the other partition from taking ownership of a shared mailslot that is already in use.

If the mailslot is not assigned to the partition, a SCSI host connected to the partition will receive a status indication from the library that the mailslot is open. When a SCSI host receives status that the mailslot is open, the application will let the operator close the mailslot or ASSIGN the mailslot to the partition. The following SCSI commands will return mailslot open status when the mailslot is not assigned to the partition or when the mailslot is actually open:

- A SCSI MOVE command to or from a mailslot element. The command will end in Check Condition Status. The sense data will indicate Not Ready, Mailslot Open (Sense Key =2h, ASC =3Ah, ASCQ =02h).

- A SCSI READ ELEMENT STATUS command that includes the mailslot elements. The command will end in GOOD status. The Import/Export Element Descriptor data for the mailslot element will return an exception condition indicating that the mailslot is open; the Except Bit will be set to 1, the ASC field will be set to 3Ah, and the ASCQ field will be set to 02h.

Table B-1 shows how the SCSI Move and SCSI Read Element Status commands are affected by the shared mailslot assignment.

Table B-1 SCSI Commands Affected by the Shared Mailslot Assignment

Mailslot Assignment | Commands from Partition 1 | Commands from Partition 2
--- | --- | ---
Unassigned | Commands will be processed as though the mailslot door is open. The following commands will report exception status: Read Element Status command that includes the mailslot element(s) Move command with source or destination set to a mailslot | Commands will be processed as though the mailslot door is open. The following commands will report exception status: Read Element Status command that includes the mailslot element(s) Move command with source or destination set to a mailslot
Assigned to Partition 1 | Commands will be processed normally. The SCSI Read Element Status and SCSI Move commands will only report that the Mailslot is open if it is physically opened and the request includes the mailslot. | Commands will be processed as though the mailslot door is open. The following commands will report exception status. Read Element Status command that includes the mailslot element(s) Move command with source or destination set to a mailslot
Assigned to Partition 2 | Commands will be processed as though the mailslot door is open. The following commands will report exception status: Read Element Status command that includes the mailslot element(s) Move command with source or destination set to a mailslot | Commands will be processed normally. The SCSI Read Element Status and SCSI Move commands will only report that the Mailslot is open if it is physically opened and the request includes the mailslot.

Note: The operator must use the UNASSIGN action in the user interface to remove the partition ownership of the mailslots when the import or export operation is complete.

The operator can open the mailslot only if it is unlocked. The locked or unlocked state of the mailslot depends on the mailslot assignment and the SCSI Prevent/Allow Medium Removal state. The library keeps separate Prevent/Allow Medium Removal data for each partition. Refer to the SCSI Prevent/Allow Medium Removal Command in the SL150 Modular Tape Library Interface Reference Manual for more details.

Table B-2 shows the conditions under which the shared mailslot is either locked or unlocked. A value of "Ignored" indicates that the Prevent/Allow Media Removal state for the associated partition does not matter.

Table B-2 Shared Mailslot Door Locked/Unlocked Conditions

Mailslot Assignment | Partition 1 Prevent/Allow Media Removal State | Partition 2 Prevent/Allow Media Removal State | Mailslot Locked State
--- | --- | --- | ---
Unassigned | Ignored | Ignored | Locked
Assigned to Partition 1 | Allowed | Ignored | Unlocked
Assigned to Partition 1 | Prevented | Ignored | Locked
Assigned to Partition 2 | Ignored | Allowed | Unlocked
Assigned to Partition 2 | Ignored | Prevented | Locked

## Partitioning—Removing the Feature

To disable the partitioning feature, simply disable partitioning on the SETTINGS screen under the Partition tab and it will revert to a non-partitioned library configuration. Only the administrator can enable or disable the partitioning feature.

After the partitions are removed, the top drive in Module 1 is configured to be the bridged drive for the non-partitioned library.