Starting named daemon in debug mode can cause problems with huge size of named.run file. By default named save debug information to /var/named/named.run file. You can stop writing to it by disabling debug mode. Check that your named runs without debug option:
ps ax|grep named named -d 3 -c /etc/named-master.conf
If -d flag exists try to restart named without it and check again
ps ax|grep named named -c /etc/named-master.conf
And that's all.
Due to data migration I'm adding here Derek's comment:
A safer way to do this is the following:
1. delete named.run (can be in /var/named, /var/cache/bind, etc, depending on the flavor of Linux).
2. "rndc notrace" to disable debug in bind
3. "rndc reload" to reopen file handles.
If you're running bind in production, killing it is not usually an option.