Device Permissons

Hello List, I´m trying to change the Permission of the Device dev/hdb2 to read/write for the Group Disk, but assoon i restart the system the defaul value is set again. I have tryed to put a rule into /etc/permission or /etc/permission.local but nothing will work. Could anybody tell me where it is written down that the devices have to have readonly for the Group Greats Michael