Enabling and disabling logical block protection

You can specify logical block protection for read and write operations, or only for write operations. You can also disable logical block protection if it is enabled. By default, logical block protection is disabled because of performance effects that result from CRC validation on the server and the tape drive.

About this task

Read/write operations to empty or filling volumes depend on whether the volumes have logical block protection. Protected and unprotected data blocks cannot be mixed on the same volume. If you change the setting for logical block protection, the change applies only to empty volumes. Filling and full volumes maintain their status of logical block protection until they are empty and ready to be refilled. For example, suppose that you disable logical block protection. If the server selects a volume that is associated with a device class that has logical block protection, the server continues writing protected data to the volume.

To enable logical block protection, specify the LBPROTECT parameter on the DEFINE DEVCLASS or the UPDATE DEVCLASS command for the 3592, LTO, and ECARTRIDGE device types:

Procedure

To enable logical block protection, specify a value of READWRITE or WRITEONLY for the LBPROTECT parameter.
For example, to specify logical block protection during read/write operations for a 3592 device class that is named 3592_lbprotect, issue the following command:
```
define devclass 3592_lbprotect library=3594 lbprotect=readwrite
```
Tips:
- If you update the value of the LBPROTECT parameter from NO to READWRITE or WRITEONLY and the server selects a filling volume without logical block protection for write operations, the server issues a message each time the volume is mounted. The message indicates that data is written to the volume without logical block protection. To prevent this message from displaying or to have Tivoli® Storage Manager write data only with logical block protection, update the access of filling volumes without logical block protection to read-only.
- To reduce the performance effects, do not specify the CRCDATA parameter on the DEFINE STGPOOL or UPDATE STGPOOL command.
- When data is validated during read operations by both the drive and by the Tivoli Storage Manager server, it can slow server performance during restore and retrieval operations. If the time that is required for restore and retrieval operations is critical, you can change the setting of the LBPROTECT parameter from READWRITE to WRITEONLY to increase the restore or retrieval speed. After data is restored or retrieved, you can reset the LBPROTECT parameter to READWRITE.
To disable logical block protection, specify a value of NO for the LBPROTECT parameter.
Restriction: If logical block protection is disabled, the server does not write to an empty tape with logical block protection. However, if a filling volume with logical block protection is selected, the server continues to write to the volume with logical block protection. To prevent the server from writing to tapes with logical block protection, change access of filling volumes with logical block protection to read-only. When data is read, the CRC on each block is not checked by either drive or the server.
If a disaster occurs and the disaster recovery site does not have drives that support logical block protection, you must set the LBPROTECT parameter to NO. If the tape drives are used for write operations, you must change the volume access for volumes with protected data to read-only to prevent the server from using the volumes.

If the server is to enable logical block protection, the server issues an error message that indicates that the drive does not support logical block protection.

What to do next

To determine whether a volume has logical block protection, issue the QUERY VOLUME command and verify the value in the field Logical Block Protection.