The filesystem group is needed for setting the filesystem permissions correctly.
The files and directories on the filesystem need to be read-writable
Therefore the file system permissions are set like this:
/scratch/lectures/MST/AVT# ls -Rlap .: total 12 drwxrws--- 3 tomcat7 avtstaff 4096 Dec 11 13:43 ./ drwxrwx--- 75 tomcat7 faw-pult-doz 4096 Dec 11 13:43 ../ drwxrwx--- 11 tomcat7 avtstaff 4096 Dec 11 13:43 2012-2013WS/ ./2012-2013WS: total 48 drwxrwx--- 11 tomcat7 avtstaff 4096 Dec 11 13:43 ./ drwxrws--- 3 tomcat7 avtstaff 4096 Dec 11 13:43 ../ drwxrwsr-x 2 tomcat7 avtstaff 4096 Dec 11 13:43 Documents/ drwxrwsr-x 2 tomcat7 avtstaff 4096 Dec 11 13:43 Exercises/ drwxrwsr-x 2 tomcat7 avtstaff 4096 Dec 11 13:43 Flash/ -rw-r--r-- 1 tomcat7 avtstaff 718 Dec 11 13:43 .htaccess.example drwxrwsr-x 2 tomcat7 avtstaff 4096 Dec 11 13:43 LectureRecordings/ drwxrwsr-x 2 tomcat7 avtstaff 4096 Dec 11 13:43 Misc/ drwxrwsr-x 2 tomcat7 avtstaff 4096 Dec 11 13:43 Podcasts/ drwxrwsr-x 2 tomcat7 avtstaff 4096 Dec 11 13:43 Rawdata/ drwxrwsr-x 2 tomcat7 avtstaff 4096 Dec 11 13:43 Slides/ drwxrwsr-x 2 tomcat7 avtstaff 4096 Dec 11 13:43 Streaming/
In this example the files are accessible for the application server (tomcat7) via the owner and accessible to the electures managers via the group (avtstaff).
Other users can't access the files, since the directory /scratch/lectures/MST/AVT/2012-2013WS are only accessible for the user and group (drwxrwx—).
So if you choose avtstaff as a filesystem group (as in this example) people accessing the file system directly need to be members of this group. The group membership is handled by your local administrator/technician and not the Electures-Portal Administrators.
You could also use faw-pult-doz as the filesystem group, but this is not recommended since that enables too many people to access the files. Currently (2012-12-11) there are 267 users in this group.
Read more about unix filesystem permissions.