Tivoli Storage Manager for Windows Administrator's Guide


Overview of Storage Area Networks (SANs)

A Storage Area Network (SAN) is a high-speed network that establishes a direct connection between storage devices and servers. This network allows tape library devices to connect at greater distances from servers, and it allows multiple servers to share the same tape library device. Figure 5 shows a SAN configuration.

Figure 5. Storage Area Network (SAN) Configuration

Storage Area Network (SAN) Configuration Drawing


TSM servers can share any library devices supported by the TSM device driver on a SAN. This includes most SCSI devices, but does not include devices using the GENERICTAPE device type.

For information about supported fibre channel hardware and configurations, visit the TSM home page at http://www.tivoli.com/support/storage_mgr/tivolimain.html .

When TSM servers share a library device, one server is the library manager and controls the library operations. These operations include mount, dismount, volume ownership, and library inventory. Other servers, library clients, use server-to-server communications to contact the library manager and request library service. See Sharing Tape Library Devices on a Storage Area Network (SAN).

TSM servers use the following features for shared library devices:

Volume Partitioning
Media volumes in the shared library device are partitioned so that only one TSM server owns a volume or the volumes are in the scratch pool. No server owns the scratch pool at any given time.

Serialized Drive Access
Only one TSM server accesses each tape drive at a time. Drive access is serialized and controlled so that servers do not dismount other servers' volumes or write to drives where other servers mount their volumes.

Serialized Mount Access
The library device's auto changer performs a single mount or dismount operation at a time. A single server (library manager) performs all mount operations to provide this serialization.

Server Operations

When the library manager server starts and the library device initializes, or after a library manager server is defined to the library client server, the library client server contacts the library manager server. The library client server confirms that the contacted server is the library manager for the named library device. The library client server also compares drive definitions with the library manager server for consistency. The library client server contacts the library manager server for each of the following operations:

Volume Mount
A library client server sends a request to the library manager server for access to a particular volume in the shared library device. For a scratch volume, the library client server specifies the volume name SCRTCH. If the library manager server cannot access the requested volume, or if scratch volumes are not available, the library manager server denies the mount request. If the mount is successful, the library manager server returns the name of the drive where the volume is mounted.

Volume Release (free to scratch)
When a library client server no longer needs to access a volume, it notifies the library manager server that the volume should be returned to the scratch pool. The library manager server database is updated with the volume's new location. The volume is deleted from the library client server volume inventory.

Table 3 shows the interaction between Library Client Servers and the Library Manager Server in executing TSM commands.

Table 3. How SAN-enabled Servers Execute Common TSM Commands

Server command Library Manager Server Library Client Server
QUERY LIBVOL Displays the volumes that are checked into the library. For private volumes, the owner server is also displayed. Not applicable.
CHECKIN/CHECKOUT LIBVOL Performs the commands to the library device. Not applicable.

When a checkin operation must be performed because of a client restore, a request is sent to the Library Manager Server.

MOVE MEDIA/MOVE DRMEDIA Only valid for volumes used by the library manager server. Requests that the Library Manager Server perform the operations. Generates a checkout process on the Library Manager Server.
AUDIT LIBRARY Performs the inventory synchronization with the library device. Performs the inventory synchronization with the Library Manager Server.
LABEL LIBVOLUME Performs the labeling and checkin of media. Not applicable.
DISMOUNT VOLUME Sends the request to the library device. Requests that the Library Manager Server perform the operation.
QUERY VOLUME Checks whether the volume is owned by the requesting library client server and checks whether the volume is in the library device. Requests that the Library Manager Server perform the operation.


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