On google I found the following page: http://www.nabble.com/Huge-latency-issue-with-8.2.6-td18947965.html
I have found in the drbdsetup (8) man page the sndbuf-size option, and I will try setting this.
On the nabble page they talk about the TCP_NODELAY and TCP_QUICKACK socket option. Does this have to do with Nagle algorithm?
Where do I set these socket options? Do I have to compile drbd with them?
those are socket flags set on a socket open() call. the page you refer to specifically says they changed this in 8.2.7