Many racks start out tidy. But after a few years of added switches, servers and “temporary” cables, they turn into a tangle nobody dares to touch. In a rack like that, unplugging the wrong cable can cut off part of the company, hot air gets trapped behind the equipment, and tracing a simple connection can take hours.
Before Installation: A Rack Plan
Standard 19-inch racks are measured in rack units (U), and each unit is about 4.45 cm tall. Before installing, decide which units each device will occupy, and leave a few units free for future expansion.
- Heavy equipment at the bottom: put the UPS, batteries and disk-heavy storage at the bottom of the rack so the center of gravity stays low and the rack does not tip over.
- Servers in the middle, on rails: install servers on their own rail kits, not stacked on top of each other.
- Network gear next to the patch panel: keep switches and patch panels close together so patch cords stay short.
- Rack depth: before buying a rack, check the depth of your servers and their rails; many rack servers do not fit in shallow racks.
Don’t Forget Airflow
Most rack servers and switches take cool air in from the front and push hot air out the back.
- Cover empty units at the front of the rack with Blanking Panels so hot air from the back does not return to the front of the equipment.
- Check the airflow direction of your switches. Some models have side or reverse airflow and must be installed to suit the rack layout.
- Cable bundles must not block the fan exhausts at the back of servers.
Network Cable Management Principles
- Use patch cords of the right length; a 3-meter cable between two adjacent devices just creates extra loops and clutter.
- Use a horizontal Cable Manager between the patch panel and the switch, and route cables along the sides of the rack with vertical cable managers.
- To bundle cables, prefer Velcro straps over plastic Cable Ties. Plastic ties damage cables when pulled tight, and every small change means cutting them off.
- Respect the cable bend radius and never kink cables; this matters even more for fiber optics.
- Define a color convention, for example one color for the user network, one for servers and one for management ports such as iLO. What matters is that the convention is consistent and documented, not the specific colors.
- Label both ends of every patch cord, and make sure the labels match the network documentation.
Separate and Duplicate Power
- Run power and network cables down opposite sides of the rack.
- Connect servers with two power supplies to two separate PDUs, and ideally feed each PDU from a separate power path or UPS. Plugging both power supplies into one power strip cancels out the redundancy.
- Use rack PDUs instead of household power strips.
- Bond the rack frame to the earth (ground) system according to electrical standards.
Before unplugging any cable in a live rack, read the labels on both ends and check its destination in the documentation. Many unplanned server room outages start with the wrong cable being pulled.
Tidying Up an Existing Messy Rack
If your current rack is a mess, you do not need to shut everything down at once:
- Document the current state: photograph the front and back of the rack and make a list of connections.
- Remove unused cables and powered-off equipment.
- Do the work in several short maintenance windows outside business hours, one switch or one server at a time.
- After each step, test access to services and update the documentation.
Checklist
- A rack unit map exists and is up to date.
- Heavy equipment is at the bottom of the rack and mounted on rails.
- Empty units are covered with Blanking Panels.
- Patch cords are short, color-coded and labeled.
- Power and network cables are kept apart.
- Dual-PSU servers are connected to two separate PDUs.
- Exhaust air at the back of equipment is not blocked by cables.
ITPlus724 engineers can review your company’s rack and server room and reorganize them with minimal service disruption.