...

Another parameter worth to consider is to so called TCP Window size, which is 64 KBytes by defaultwindow size. By default BBCP would set it to 64 KBytes. The corresponding option for bbcp is called "-w". In the following example, the desired window size is set to 2 MBytes:

% bbcp -P 2 -w 2M localhost:/dev/zero /dev/null
user@localhost's password:
bbcp: Creating /dev/null/zero
bbcp: At 090413 18:12:04 copy 0% complete; 113401.7 KB/s
bbcp: At 090413 18:12:06 copy 0% complete; 113695.8 KB/s
bbcp: At 090413 18:12:08 copy 0% complete; 113981.2 KB/s
..

Note, that both machines (operating systems) involved into the transfer should allow setting this parameter above the default value. See the *Tuneup" section below for further details on this subject.

The best performance would be achieved by setting optimal values for both TCP window size and a number of sumultaneous streams. One would need to experiment with these paramaters for a specific network/system setup.

3 Troubleshooting

No bbcp executable available at a remote site

...

% bbcp -z -P 2 user@SomeRemoteHost:/dev/zero /dev/null
user@SomeRemoteHost's password:
bbcp: Creating /dev/null/zero
bbcp: At 090414 02:59:48 copy 0% complete; 5461.3 KB/s
bbcp: At 090414 02:59:50 copy 0% complete; 13639.7 KB/s
..

4 Tuneup

Choosing an optimal value for TCP window size

The general rules of "thumb" are:

• the higher the RTT time is - the bigger the window should be
• the "bumbier" (higher probability of dropping packets en-route) network is - the smaller the window should be

5 Usefull links

• http://pcbunn.cithep.caltech.edu/bbcp/using_bbcp.htm - the link provides usefull tips on tuning up TCP parameters on machines involved into the data transfer.