Size values for shared data buffers
Table: Byte values for SIZE_DATA_BUFFERS_xxxx files lists appropriate values for the various SIZE_DATA_BUFFERS files. The integer represents the size of one tape or disk buffer in bytes. For example, to use a shared data buffer size of 64 kilobytes, the file would contain the integer 65536.
These values are multiples of 1024. If you enter a value that is not a multiple of 1024, NetBackup rounds it down to the nearest multiple of 1024. For example, if you enter a value of 262656, NetBackup uses the value of 262144.
The NetBackup daemons do not have to be restarted for the parameter values to be used. Each time a new job starts, bptm checks the configuration file and adjusts its behavior.
Analyze the buffer usage by checking the bptm debug log before and after you alter the size of buffer parameters. Note that the bptm log applies to both tape backups and disk backups.
Table: Byte values for SIZE_DATA_BUFFERS_xxxx files
Kilobytes per data buffer | SIZE_DATA_BUFFER value in bytes |
|---|---|
32 | 32768 |
64 | 65536 |
96 | 98304 |
128 | 131072 |
160 | 163840 |
192 | 196608 |
224 | 229376 |
256 | 262144 |
Important: the data buffer size equals the tape I/O size. Therefore the SIZE_DATA_BUFFERS value must not exceed the maximum tape I/O size that the tape drive or operating system supports. This value is usually 256 kilobytes or 128 kilobytes. Check your operating system and hardware documentation for the maximum values. Take into consideration the total system resources and the entire network. The Maximum Transmission Unit (MTU) for the LAN network may also have to be changed. NetBackup expects the value for NET_BUFFER_SZ and SIZE_DATA_BUFFERS to be in bytes. For 32K, use 32768 (32 x 1024).
Note:
Some Windows tape devices cannot write with block sizes higher than 65536 (64 kilobytes). Some Windows media servers cannot read backups on a Linux/UNIX media server with SIZE_DATA_BUFFERS set to more than 65536. The Windows media server would not be able to import or restore images from media that were written with SIZE_DATA_BUFFERS greater than 65536.
Note:
The size of the shared data buffers for a restore is determined by the size of the shared data buffers in use at the time the backup was written. Restores do not use the SIZE_DATA_BUFFERS files.