Backbone Redundancy for a Campus Data Center
A financial services firm is consolidating two data centers into a new facility. The design includes an MC and two intermediate cross-connects (ICs) on separate floors. The owner requires no single point of failure for the backbone between the MC and each IC. The contractor proposes a single 24-strand OS2 backbone from the MC to each IC, routed in the same conduit and tray for the entire path, with a spare pair for future growth. The building has diverse entrance facilities but the intra-building pathway is shared. The firm's auditors have asked for evidence of pathway diversity.
1. Evaluate whether the proposed backbone meets the no-single-point-of-failure requirement.
Read the worked answer
It does not. A single cable in a single pathway is a single point of failure regardless of strand count. Meeting the requirement needs physically diverse pathways (separate routes, separated by distance and preferably fire compartments) and separate cables, with each path capable of carrying the required load. Spare strands provide capacity, not redundancy. The design must specify diverse routing and demonstrate it on drawings.
2. What documentation should be produced to satisfy the auditors?
Read the worked answer
Provide pathway drawings showing physically separate routes from MC to each IC, cable schedules identifying each backbone cable and its route, and a narrative describing separation distances and fire compartment boundaries. Include test results for each cable and a redundancy statement mapping each critical circuit to its primary and alternate path. The documentation must match as-built conditions, so it should be updated after installation and verified during commissioning.
3. The contractor says diverse routing will add 30% to pathway cost. How do you advise the owner?
Read the worked answer
Present the cost against the stated requirement and the operational consequence of a shared-path failure: simultaneous loss of both backbone legs during a single event (e.g., construction strike, fire, or water). Offer options: full diverse routing, partial diversity with one path in a rated enclosure, or accepting the risk with documented owner sign-off. The decision belongs to the owner, but the designer must make the trade-off explicit and record it.