Know more about THE IEEE 1244 STANDARD FOR REMOVABLE MEDIA MANAGEMENT Operational characteristics of the media manager

Know more about THE IEEE 1244 STANDARD FOR REMOVABLE MEDIA MANAGEMENT  Operational characteristics of the media manager

From the point of view of the client, the media manager works as a server that waits for MMP commands, which the client sends via a TCP/IP connection. The media manage executes these commands, generates appropriate responses and sends these back to the clients. All commands are given unambiguous task identifiers. The responses contain the task identifier of the command in question. The response takes place in two stages. First, the successful receipt of the command is acknowledged. In a second response, the application is informed whether the command has been successfully executed and which responses the system has supplied. Example 1 An application wants to mount the volume with the name back-up-1999-12 31. To this end it, sends the following command to the media manager: mount task[' '1' '] volname [' 'back-up-1999-12-31' ']

report [MOUNTLOGICAL.' 'MountLogicalHandle' ']; The media manager has recognized the command and accepted it for processing and

therefore sends the following response: response task[' '1' '] accepted; Now the media manager will transport the cartridge containing the volume into a drive to which the application has access. Once the cartridge has been successfully inserted, a response is generated that could look like this:

response task[' '1' '] success text [' '/dev/rmt0' ']; The media manager stores all commands in a task queue until all resources required for execution are available. Once all the resources are available, the media manager removes the command from the task queue and executes it. If several commands are present that require the same resources, the media manager selects the next command to be carried out on the basis of priorities or on a first come, first served basis. All other commands remain in the task queue until the resources in question become free again. In this manner

libraries, drives and also cartridges can be shared. Commands that are in the task queue can be removed again using the Cancel command

Operational characteristics of the library and drive managers The library manager receives the media manager's commands via the library manage

ment protocol (LMP) and converts these into the specific commands for the hardware in question. From the point of view of the media manager, a unified abstract interface tha conceals the properties of the hardware in question thus exists for all libraries. New hard ware can thus be integrated into the management system using a suitable library manager without having to make changes to the whole system. Accordingly, drive manager implementations of the abstract drive management protocol (DMP) are interfaces for a certain drive hardware. However, drive management

must also take into account the specific properties of the various client platforms upon which the applications that want to use the media management system run. If such an application is running on a UNIX-compatible platform, the drive manager must provide the corresponding names of a device special file for access to the drive. Under Windows, such a drive manager must supply a windows-specific file name, such as \\.\TAPE0.

Privileged and non-privileged clients The media manager carries out requests from clients that want to take advantage of the media management services. From the point of view of the media manager there are privileged and non-privileged clients:

• Non-privileged clients, such as back-up systems, can only handle objects for which they have been granted an appropriate authorization.

• Privileged clients, usually administrative applications, may perform all actions and manipulate all objects. They serve primarily to include non-privileged applications in the system and to establish suitable access controls.  The IEEE 1244 data model (Table 9.1) In addition to the architecture and the logs for communication, the standard also describes a complete data model, which includes all objects, and their attributes, that are necessary for the representation of the media management system. Objects can be provided with additional application-specific attributes. The object model can thus be dynamically and flexibly adapted to the task at hand, without changes being necessary to the underlying management system. 9.5.3 Media Management Protocol (MMP) The media management protocol (MMP) is used by the applications to make use of

the media management services of an IEEE 1244-compatible system. MMP is a text based protocol, which exchanges messages over TCP/IP. The syntax and semantics of the individual protocol messages are specified in the MMP specification IEEE 1244.3. MMP permits applications to allocate and mount volumes, read and write metadata and to manage and share libraries and drives platform-independently. Due to the additional bstraction levels, the application is decoupled from the direct control of the hardware. Thus, applications can be developed independently of the capability of the connected hard- ware and can be made available to a large number of different types of removable media.

Table 9.1 The most important objects of the IEEE 1244 data model

Object Description

APPLICATION Authorized client application. Access control is performed on the basis of applications. User management is not part of this standard, since it is assumed that it is not individual users, but applications that already manage their users, that will

use the services of the media management system.  AI Authorized instances of a client application. All instances of an application have unrestricted access to resources that are assigned to the application. LIBRARY Automatic or manually operated libraries.

LM Library managers know the details of a library. The library manager protocol serves as a hardware-independent interface between media

manager and library manager. BAY Part of a LIBRARY (contains DRIVES and SLOTS). SLOT Individual storage space for CARTRIDGEs within a

BAY. SLOTGROUP Group of SLOTS to represent a magazine, for example, within a LIBRARY. SLOTTYPE Valid types for SLOTs, for example 'LTO',

'DL-Tor3480', 'QIC' or 'CDROM'. DRIVE Drives, which can accept CARTRIDGEs for writing or reading. DRIVEGROUP Groups of drives.

DRIVEGROUPAPPLICATION This object makes it possible for applications to access drives in a DRIVEGROUP. This connection can be assigned a priority so that several DRIVEGROUPs with different priorities are available. The media manager selects a suitable drive according to priority.

DM Drive manager. Drive managers know the details of a drive and make this available to the media manager. The drive manager protocol serves as a hardware-independent interface between media manager and drive manager. CARTRIDGE Removable data carrier; media. CARTRIDGEGROUP Group of CARTRIDGEs. CARTRIDGEGROUPAPPLICATION This object makes it possible for applications to access CARTRIDGEs in a CARTRIDGEGROUP.

This connection can be assigned a priority so that several CARTRIDGEGROUPs with different priorities are available. The media manager selects a

suitable CARTRIDGE according to priority in order to allocate a VOLUME, if no further entries are made. (continued overleaf )