Element Numbering

The element numbering in the TS4300 provides a unique identifier for important library elements.

These numbers are used in library interfaces and software to address and locate a particular library element.

The following library elements are numbered:

  • Modules (Library Base and Expansion modules)
  • Slots (storage and I/O)
  • Drives

Library Element Numbering

Three different numbering systems are used to identify elements in the library. These different number schemes offer flexibility in communicating the expandable configuration of the library to the customer, to service, and to attached systems.

  1. Logical element numbering
  2. Physical element numbering
  3. SCSI element addressing

Logical Numbering, also referred to as ‘Logical ID’ or just ‘ID’, is the primary method used in library interfaces and logs to identify each unique element. Elements are numbered from the bottom up in sequential fashion, as they appear in the configured library.

Figure 1. Logical Numbering Example for a 3-module library

Physical Element Numbering

A Physical Number, abbreviated as "Phy Num" or "PNUM, is also assigned to each element. Unlike Logical Numbering, the PNUM is based on an element’s position in a physical library configuration, from the bottom up. PNUMs are used by the software for internal use only and are typically useful in complex troubleshooting. The PNUM are often listed next to the Log ID, in parentheses, as a diagnostic aid in library logs or interfaces.
Figure 2. Physical Numbering Example for a 3-module library

SCSI Element Addressing

SCSI Element Addressing, defined by industry SCSI standards, assigns identifiers to library elements that are used by software applications. Element Addresses are derived from PNUM, but altered as defined by SCSI specifications.

  • Drive element addresses start at 1 with the bottom drive that is installed in the library
  • I/O slot element addresses start at 101 with the bottom I/O slot in the library
  • Cartridge Slot element addresses start with 1001 at the bottom slot in the library
  • Modules are not assigned a SCSI address
SCSI element addresses appear in logs and library interfaces along with Element IDs and PNUMs.
Figure 3. SCSI addressing example for a 3-module library

Library Elements Numbering Details

These three numbering scheme present differently across the three numbered elements of a library: modules, slots, and drives.

Library Module Numbering

Modules have Logical IDs and Physical Numbers. They do not have SCSI Element addresses. Module numbering can be viewed in the Library Menu of the Navigation Dock in the Management GUI.

Module Logical ID: Module IDs are assigned during configuration in the library start-up process. Modules are numbered from bottom to top starting with '1'. Each Module ID, including the base module, is assigned based on its position in the library.

Example: in a 5-module library, the bottom module ID is 1 and the top module ID is 5. If a module is defective or was removed for repair, the numbering of the modules does not change until the library is restarted. When the library is started again, it goes through a configuration process that includes renumbering of modules

Module Physical Number (PNUM): The physical number is based on the position of the module relative to the base module. In a 21U Library, the base always has a PNUM of 4. In a 48U library, the base always has a PNUM of 9. Expansion modules above the base module have higher PNUMs. Expansion modules below the base module have lower PNUMs. Refer to Differences between 21U and 48U libraries to determine if the library is a 21U or 48U library.

Cartridge Slot and I/O Magazine Slot Numbering

Slot numbering uses all three numbering systems to identify slots inside the library: Logical ID, Physical Number, and SCSI Element address. Slot numbering can be viewed in the graphical library view or in the Management GUI.

Cartridge Slot Logical ID: The slot ID is generated by combining the Module Logical ID of the module where the slot is and the position of the slot in the module. The position ranges from 1 to 40 and are assigned sequentially, from bottom to top, left to right. Refer to Figure 1 for a visual representation.

The format is [Module].[Slot]. Example: ID 2.7 is Module 2, slot 7.

The Slot ID determination is not dependent on I/O Station configuration. A particular slot will always have the same ID, independent if it is a standard storage slot or an I/O magazine slot. This avoids having to renumber of all slots in a library if I/O Station slots are enabled or disabled in any module.

Cartridge Slot Physical Number (PNUM): Slot Physical Numbers are sequential numbers that are assigned relative to a full library stack. They start at 1 with the first possible slot at the bottom of a full library stack. They end with the last possible slot at the top of a full library stack. Default slot PNUMs in the base modules are different in a 21U versus a 48U Library. The PNUM of the first slot in a 48U base module is 321. The PNUM of the first slot in a 21U Library base module is 121. Slots in expansion modules above the base module have higher PNUMs. Slots in expansion modules below the base have lower PNUMs. Refer to Differences between 21U and 48U libraries to determine if the library is a 21U or 48U library.

Cartridge Slot SCSI element address: SCSI element addresses are counted in the same order as the Slot PNUM. SCSI element addresses are separately assigned to I/O slots and cartridge slots for each library partition. SCSI initiators can change SCSI element addresses by using the element assignment mode page. SCSI element addresses are counted in the same order as the Slot PNUM. Slot PNUM and element addresses might not be contiguous if mail slots are enabled in the middle of a partition.

Drive Numbering

Drive numbering uses all three numbering systems to identify drives inside the library: Logical ID, Physical Number, and SCSI Element address. Drive numbering can be viewed in the graphical library view or in the Management GUI.

Drive Logical ID: Drives are numbered from bottom to top, starting with 1. Only drives that are present in the library are counted. Adding or removing drives can result in a change of drive logical numbers.

Drive Physical Number (PNUM): Drive PNUMs start with the lowest drive bay (drive sled connector) in a library. The numbering proceeds upward to the highest drive bay. Drives have the PNUM of the drive bay in which they are installed. Full High tape drives occupy two drive bays, but they are numbered by using the lower bay where they plug into the library. The PNUM of the upper bay behind a full high drive is never assigned to a drive. Assignment of World Wide Name (WWN) or World Wide Identifier (WWID) and serial number spoofing is based on the drive PNUM.

Drive SCSI element address: SCSI element addresses are separately assigned for each library partition. SCSI initiators can change element addresses by using the element assignment mode page. SCSI element addresses are numbered in the same order as the Drive IDs. Gaps are not allowed in SCSI element addresses.

Adding or Removing a Drive: When drives in the library are added or removed, the renumbering of the drives may not be immediate or automatic When a drive is physically removed, the drive remains in the library configuration, but the drive is described as "removed" and is not accessible to the host. Persistence of a drive number after removal is done to maintain connectivity with software that is configured to the drives. The software anticipates the original drive or a new drive will be installed shortly.

The drives are renumbered under the following conditions:
  • Logical and Physical Numbering is updated automatically when a drive is installed, and cartridges can be loaded or unloaded from the added drives.
  • SCSI Element addressing does not change until a partitioning wizard is run to move the added drive into a partition.
  • The "Reset the List of Known Drives and Modules" (Settings > Library > Advanced) function is used. Resetting the "list of known drives and modules" causes the library to inventory the drives and modules that are physically present. This operation alters the list of SCSI element addresses reported to hosts and renumbers the drives and modules. This operation cannot be undone. After the operation completes, use one of the logical library wizards to modify logical libraries as needed.
  • Power down or reset does not change drive numbering, but factory reset changes updates the numbering when the partitioning wizard runs as part of the reset process.

Other Library Elements

Library controller cards and power supplies are not numbered individually. Their identifier is the module number in which they are located. Some modules might contain two power supplies, an upper one and a lower one. The library does not provide any identification to differentiate between an upper and lower power supply.

Logical Libraries

Configuring logical libraries does not change the ID or PNUM, but it does change the SCSI element addresses.