Q:

Having user1's home direcrory on internal hdd and user2' home direcrory on external hdd?

Does anybody know if it is possible to have the home folder of one user, for example; /home/user1 on internal hdd and when i log in with user2 the /home/user2 on external hdd?

A:

The user's HOME directory is set upon user login, from the 6th colon separated field in the user's /etc/passwd entry. For example, MY /etc/passwd file contains these users: 
walt2:x:1001:1000:Walt2 Sullivan,,,:/home/walt2:/bin/bash
walt:x:1000:1000:Walt Sullivan,,,:/home/walt:/bin/bash

User walt2's HOME directory is /home/walt2, and walt's HOME directory is /home/walt. They could be anywhere that is mounted at the beginning of the user's login.  
Read man 5 passwd and man vipw (always use vipw to edit the passwd - it can use any EDITOR, not only vi). 

