sshd responsiveness

[Carsten Mattner]

When I compared FreeBSD 9.1 geli based full disk encrypted system
with a dfly (HAMMER) 3.2.2 full disk encrypted system I noticed that
using an ssh session is considerably less responsive on dfly if I
rsync data from another machine to the dfly machine in parallel.
On FreeBSD the ssh session doesn't get unresponsive. This is
subjective and not scientifically measured and I'm just curious
to hear your thoughts. Is it just probably caused by default settings?