Try some tuning, that should help you to get a better performance:

1) Try to tune the Jumbo Frames to 9000 (If you have 10GbE NICs), you can go to the Console mode, Hardware Tools
(Ctl - Alt - W), Select Tuning Options Select Jumbo Frames Config.

2) Try to make a Drbd tuning, the following values may help you:
max-buffers=8000
max-epoch-size=8000
unplug-watermark=8000
no-disk-barrier=on
no-disk-flushes=on

Also you can find the following useful link:
http://www.drbd.org/users-guide/s-th...ut-tuning.html