What is the use of Tivoli Storage Manager (TSM) SANDISCOVERY Server option ?


Tivoli Storage Manager (TSM) has a new server option called SANDISCOVERY from version 5.3which allows TSM Server to check automatically if the attached SAN devices has changed their configuration information. When this option is set to ON, the server will perform SAN discovery in the following instances:
  • During server initialization
  • When the device path has been changed
  • When the QUERY SAN command is issued

What is SANDISCOVERY ?

The SANDISCOVERY option specifies whether the Tivoli Storage Manager SAN discovery function is enabled. Using SAN discovery, the server can automatically correct the device's special file name if it has been changed.

Also Read: Storage Area Network (SAN) Basic Free Tutorials


To use SAN discovery, all devices on the SAN must have a unique worldwide name (WWN). Some virtual tape libraries use the same WWN for all of their drives, SAN discovery will fail for these libraries. If this happens, set the SANDISCOVERY option to OFF and manually define or update the drive paths. If the virtual tape library provides no WWNs, SAN discovery will attempt to use serial numbers to identify the drives.

>>-SANDISCOVERY--+-ON------+-----------------------------------><
    +-OFF-----+        '-PASSIVE-'   

Parameters

ON
With this option specified, the server will perform SAN discovery during server initialization, when the device path has been changed, or when the QUERY SAN command is issued. This is the default.

OFF
With this option specified, the server will not perform SAN discovery during the server initialization, when the device path has been changed, or when the QUERY SAN command is issued. This is the default.

PASSIVE
With this option specified, the server will not perform SAN discovery during server initialization, when the device path has been changed, or when the QUERY SAN command is issued. This conceals the message produced when you disable SAN discovery and does not take device paths off-line.
The SAN environment can shift dramatically due to device or cabling changes. Device IDs assigned by the SAN may be altered due to bus resets or other environmental changes. This "dynamically" changing nature of the SAN can cause the "static" definitions defined and known to the server (or storage agent) to fail or become unpredictable.



For instance, the server may know a device as id=1 based on the original path specification to the server and original configuration of the LAN. However, some event in the SAN (new device added, cabling change) causes the device to be assigned id=2. When the server tries to access the device with id=1, it will either get a failure or the wrong target device. The server assists in recovering from changes to devices on the SAN by using serial numbers to confirm the identity of devices it contacts.

When you define a device (drive or library) you have the option of specifying the serial number for that device. If you do not specify the serial number when you define the device, the server obtains the serial number when you define the path for the device. In either case, the server then has the serial number in its database. From then on, the server uses the serial number to confirm the identity of a device for operations.

When the server uses drives and libraries on a SAN, the server attempts to verify that the device it is using is the correct device. The server contacts the device by using the device name in the path that you defined for it. The server then requests the serial number from the device, and compares that serial number with the serial number stored in the server database for that device.

If the serial number does not match, the server begins the process of discovery on the SAN to attempt to find the device with the matching serial number. If the server finds the device with the matching serial number, it corrects the definition of the path in the server's database by updating the device name in that path. The server issues a message with information about the change made to the device.

Then the server proceeds to use the device. You can monitor the activity log for messages if you want to know when device changes on the SAN have affected Tivoli Storage Manager. The following are the number ranges for messages related to serial numbers:

 ANR8952 through ANR8958
 ANR8961 through ANR8968 
Restriction: Some devices do not have the capability of reporting their serial numbers to applications such as the Tivoli Storage Manager server. If the server cannot obtain the serial number from a device, it cannot assist you with changes to that device's location on the SAN.




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