Setting the network buffer size for the NetBackup media server

A modern, well configured, operating system with properly written TCP drivers is unlikely to need TCP memory tuning by NetBackup. Accordingly, the best NetBackup configuration is to disable tuning by placing a zero (0) into the NET_BUFFER_SZ file on media servers and Linux/UNIX clients. Simply deleting the file is not equivalent because some NetBackup processes have default setsockopt API calls configured to overcome past external problems with various platforms and drivers. See the following paragraphs for more details and other considerations.

NET_BUFFER_SZ is a tunable media server parameter that can be used to adjust the size of the network buffer space. The operating system uses this buffer space for the connection between the bptm child process and the client process. This buffer space caches either received data from the network (a backup) or written data to the network (a restore). The parameter sets the value for NetBackup to use for the network buffer space, but the operating system may not allow the change.

The NetBackup media server can be configured to request that the operating system use a non-default size for the network buffer space. If the NET_BUFFER_SZ touch file exists, bptm requests that the operating system adjust the size. The operating system may or may not allow the change, depending on the operating system revision and the current TCP tuning.

The following examples are from bptm logs on various platforms. These examples show how bptm records the size that was used and any previous size requested by NetBackup.

For example:

Red Hat

setting receive network buffer to 1049600 bytes

Solaris 10

setting receive network buffer to 65536 bytes
receive network buffer is 64240 bytes

Windows

setting receive network buffer to 1049600 bytes
setting receive network buffer to 1049600 bytes

The default value for this parameter is derived from the NetBackup data buffer size using the following formula:

For backup jobs: (<data_buffer_size> * 4) + 1024

For restore jobs: (<data_buffer_size> * 2) + 1024

For tape:

If the default value for the NetBackup data buffer size is 65536 bytes, the formula results in the following: a default NetBackup network buffer size of 263168 bytes for backups and 132096 bytes for restores.

For disk:

If the default value for the NetBackup data buffer size is 262144 bytes, the formula results in the following: a default NetBackup network buffer size of 1049600 bytes for backups and 525312 bytes for restores.