Recommended shared memory settings

The SIZE_DATA_BUFFERS setting for backup to tape is typically increased to 256 KB and NUMBER_DATA_BUFFERS is increased to 16. To configure NetBackup to use 16 x 256-KB data buffers, specify 262144 (256 x 1024) in SIZE_DATA_BUFFERS and 16 in NUMBER_DATA_BUFFERS.

Note that an increase in the size and number of the data buffers uses up more shared memory, which is a limited system resource. The total amount of shared memory that is used for each tape drive is:

Shared memory = (number_data_buffers * size_data_buffers) * number_tape_drives * max_multiplexing_setting

For two tape drives, each with a multiplexing setting of 4 and with 16 buffers of 256KB, the total shared memory usage would be:

(16 * 262144) * 2 * 4 = 32768 KB (32 MB)

If large amounts of memory are to be allocated, the kernel may require additional tuning to provide enough shared memory for NetBackup.

Make changes carefully, monitoring for performance changes with each modification. For example, an increase in the tape buffer size can cause some backups to run slower. Also, there have been cases with restore issues. After any changes, be sure to include restores as part of your validation testing.