Edit: This is still relevant information to consider.
Originally posted February 15, 2011 on AIXchange
I recently shared some of my gripes concerning modern data centers, as well as the importance of keeping actual people in mind when designing and constructing these buildings.
On a somewhat related note, another trend I’m seeing is those nice new, pristine racks become a nightmare once it’s time to service the equipment.
I’ve seen plenty of newly constructed raised floors. These facilities look marvelous. The cables are all color-coordinated and very neatly laid out. They’re cut to precise lengths (no slack) and tied down from the switch, through the cable management trays, into the cable management arms and into the server. The people that tour these places must go away thinking that any company that goes to these lengths to organize its IT equipment this organized must be on top of its entire operation.
The problem is, raised floors aren’t meant to be pretty. When the cabling is that precise, it can actually be a problem. For instance, without the slack, you can no longer slide the drawers forward in the rack to service the components.
IBM has quite a few hot swap parts in their computers. They have great rails that they use to mount their servers in the computer racks, and these rails allow you to easily slide a drawer in and out of the rack. (Aside: I find that the latest design for the HMC and the POWER7 rails is the easiest to install, while the rails for some storage switches which shall remain nameless are the worst. The last thing I want to do when installing switches is assemble rails.)
Anyway, here’s the big deal with cables cut to size: When your machine needs service, the only way you can slide it forward and fix it is to unplug everything. The machines have rails for a reason — so you can move them a bit to tinker with them when necessary. If you tie down your cables without leaving slack, you defeat the purpose of having these redundant hot swap parts for the machines.
If I need to unplug everything to service a machine, I have to be careful to avoid bumping into the other servers, and I need to hope that the cables are labeled properly so that they get plugged in correctly when the service is over. When you’re talking about multiple adapters, multiple connections and multiple serial and HMC cables, that’s not a trivial number of connections.
Another interesting thing I see is some people not using any rails. They just put shelves into their racks and stack two or three servers on a shelf. I don’t think this is any better. I still cannot slide the machines out, and worse, if I need to reach one of the bottom machines, I may need to power off multiple physical servers just to get at it.
Cleanliness has its place in the computer room, of course. You should make sure your racks and cabling are clean. But think about what you actually need and, literally, cut your service personnel some slack — make sure there’s enough slack in the cables that each drawer can be easily pulled out when service is needed.