If login is not working on ftp, it is not seemingly random, it is an authentication issue. If you have 8 gig of memory and it's shared by 512 mbytes, you assume immediately that the problem is ram. Why so?
On home systems, it is often unnecessary to buy 2x6 core xeon with 48gigabytes memory, just to serve 4 disk pool on gigabit network with realtek cards...