Duplication speed with staging / parallel process

The pbx process is not responsible for read or write processing.

It will be bptm process on the destination server as well as bptm processes on the source server.

You may want to create bptm log folders on both servers to see what the current buffer sizes are and on which side the 'wait for full' or 'wait for empty' buffers are.

About Buffer Tuning, see:

NetBackup Backup Planning and Performance Tuning Guide, Release 7.5 and Release 7.6 : 
http://www.symantec.com/docs/DOC7449

These might be a good start (on both source and destination)

echo 128 > INSTALL_PATH\Veritas\NetBackup\db\config\NUMBER_DATA_BUFFERS
echo 128 > INSTALL_PATH\Veritas\NetBackup\db\config\NUMBER_DATA_BUFFERS_DISK
echo 262144 > INSTALL_PATH\Veritas\NetBackup\db\config\SIZE_DATA_BUFFERS
echo 524288 > INSTALL_PATH\Veritas\NetBackup\db\config\SIZE_DATA_BUFFERS_DISK

Play around with the numbers after you've read the guide that Marianne posted.