How should be security implemented in a datacenter? I wish to know not about the network security but the physical security aspects, like unauthorised access to the systems and likewise.
utilize a man trap for access.
24x7 NOC provides escort access to the DC floor. NOC holds cage or rack keys.
Cameras in the aisles without obstructions ie. doors.
Look for the DC to have a SAS 70 Type 2 certification and in most cases you will be pretty safe.