[Samba] How many memory do I need with the samba4 dc?

[Sense Zeng]

My AD is using  win2003 DC now. Domain functional level and Forest
functional level are 2003. I try to use the samba4 server replace the
win2003 server.
User account: 6044
Group: 111
Computer account: about 1000
I tried use a computer (system: ubuntu 13.10) with 1G ram to join domain as
DC (samba-tool domain join ... DC ...) and 1G ram gone fast. Samba-tool
domain join did not success.
How many memory do I need as my AD with the samba4 DC server?