I have found this problem with all rh6.x versions, I don't know if it is applicable to other versions. My system has about 3000 active accounts. The problem is: The variable displayed with $ cat /proc/sys/fs/dquot-nr Increments until system hangs when this value is equal to /proc/sys/fs/dquot-max (default 1024). A temporary workaround is increment this value. Rebooting the system dquot-nr returns to 0 and starts incrementing again.
This from the kernel documentation: dquot-nr and dquot-max The file dquot-max shows the maximum number of cached disk quota entries. The file dquot-nr shows the number of allocated disk quota entries and the number of free disk quota entries. If the number of free cached disk quotas is very low and you have a large number of simultaneous system users, you might want to raise the limit. Of course, it shouldn't hang when this resource gets low, but you might find that: echo 4096 > /proc/sys/fs/dquot-max in /etc/rc.d/rc.local will solve your problems.
this is a kernel issue. Is it still present in RH7 (2.2.16 and later) kernels?