The same MAXBFRU value is used for each of the READ subchannels. The resulting buffer size is number_of_pages multiplied by 4K. The total buffer space used is 4K times number_of_pages, times the number of READ subchannels.
If there is a hardware buffer size for MPC, VTAM® compares the MAXBFRU value and the hardware buffer size and uses the smaller of the two to avoid wasting fixed storage. MAXBFRU is not used to determine the buffer size of the WRITE subchannels coded on this host. The WRITE subchannel buffer size is determined dynamically by VTAM depending on the setting at the READ end of the channel.
You can reduce this value after examining VTAM multipath channel tuning statistics so that excessive storage is not allocated for each subchannel. To obtain tuning statistics output, code the TNSTAT start option or use the MODIFY TNSTAT command. See the z/OS Communications Server: SNA Network Implementation Guide for more information on MPC tuning statistics.