By default, the maximum number of open fd descriptors is pretty low.
Please see this article on how to increase it.
As reported in this bug report (http://bug.flexraid.com/view.php?id=195), changing the user level limit seems to have the most effect.
As per the comments in that report, the user had to add the following to /etc/security/limits.conf (root being the user in this case):
root soft nofile 4096
root hard nofile 10240