"Know what you're building" seems like an obvious thing to say, but I don't think we do it that well in IT. For my recent data centre relocation project, we applied that principle successfully to a couple of areas. The network lead wrote up exactly what he was building, and the storage lead listed out every device he needed. But we never did a complete "final state" description of the new data centre.

It all worked pretty well, although we needed a number of meetings during the design phase of our new data centre -- laying out the racks, non-rack equipment, power, cabling for the networks. I think we needed to have a lot of meetings because there isn't a commonly accepted way to draw a plan of a data centre that covers the requirements of all the people in the room.

I'm running into the issue again in a smaller way now that we're designing the new central communication room for the equipment that used to be in the old data centre, but needs to remain behind for local operations (mostly the network gear to service a large office building).

Just as a refresher, here are all the people you need to involve:

  • The server team(s) know the physical dimensions of the servers, their weight, how many network ports they have and how they need to be configured, whether they need SAN-attached storage, backup requirements, how much power and cooling the server needs
  • The network team(s) know the network devices, which have most of the same requirements as servers, the approach for connecting, which defines the need for cables and patch panels, and the cabling, which may affect weight of cable trays or floor loading
  • The storage team(s) know the switching devices, which have most of the same requirements as the network devices
  • The electrical engineer or consultant needs to know all the power requirements and placement of all the equipment
  • The mechanical engineer or consultant needs to know the cooling requirements and placement of all the equipment
  • The structural engineer or consultant needs to know the weight and placement of all the equipment
  • The trades who actually build it all need to know exactly what they're building
  • There's likely some other poor person, maybe a building architect, who has to pull this all together

Add to all that the fact that the technology in a data centre is constantly changing, at least in terms of the number and type of servers in the room. Also, the requirements and constraints tend to be circular: For example, the number of network ports on a server affects the amount of network gear you need, which affects how many servers you can have (either through port capacity or rack space), which affects how much power and cooling you need but also how many network ports you need.

You also have to worry about other details than can seriously derail an otherwise great plan. For example, when running fibre, you need to make sure it's the right kind of fibre and that it has the right connectors. Power cables in a data centre can be varied, so again you need to make sure that the power distribution units (PDUs) in the racks can be connected to your servers.

With all this, it can be hard for people to come to an agreement on what to build. We don't have well-established ways of describing what's going to be built in a way that everyone understands. There's software to help do this, but it tends to be unreasonably expensive for a medium-sized enterprise.

Regardless of how hard or expensive it is, there's a lot of value in figuring out what you're going to build, before you built it. We were successful using Excel and Word to describe what to build, and drawings of floor plans. We had to be extremely careful about versions and keeping the different documents in sync. In the end, happily it all worked out.