Filling The Void

Now that I have decided to go all the way and try to stuff 160 machines into a single cabinet, I needed to think about the rest of the stuff that makes the machines work, like power, ethernet, cooling, etc… Until now I had only given this a slight thought, I know I would need network switches in the cabinet, but now I know I need 4 — 48 Port Gigabit ehternet switches, 9 PDU’s, a NetBoot Server (Xserve) and some fans to prevent it from becoming less of a Mac Mini rack and more of an aluminum smelter.

The racks have 45 Rack Units “U” available, that mean I had room for 40 shelves of Mac Mini’s, 4 1U Network Switches and one XServe for NetBooting, but where in the world was I going to fit 9 PDU’s!!!! They were not going to fit, no matter how hard I tried, there was just not enough room (and these are the 0U PDU’s that hang vertically at the back of the cabinet… and I only had room for 4 at the most. I had to engineer something different. I had seen in the past some vendors included “Y” power cable splitters with their multi-power supply servers, I thought why not do something like that for the Mac Mini’s? The Mac Mini’s only draw 40 watts, that’s nothing. I could run at least 8 from a single plug, maybe more, but I still wanted to be safe.  I had to figure out how to physically plug 160 machines. Working with vendors and because the power draw of the mini’s was so low, we were able to design a 4 to 1 cable allowing me to plug 4 mini’s in using a power outlet on the PDU.

And a finished sample::

20120918-0905162 copy

Also, I had another issue, these machines were going to be in a datacenter 45 minutes away from my office. Traditionally, I would rely on two tools to help manage remote servers, one was IPMI, and the other was remote power management through a managed PDU. Both of these methods allow me to cut power to a machine so it can reboot if in a stuck state, but I was about to lose both of these tools, the IPMI didn’t exist, and the Mac Mini was engineered in such a way that it was “Supposed” to power itself back up after losing power, but it didn’t work if the machine was hung when the power was cut, so that was useless… I had to come up with a solution. On went the engineering hat and I came up with the idea of attaching a micro hobby servo to each Mac Mini when controlled by a “Phidget” servo controller and some custom code I wrote allowed me to have total control over the Mac Mini’s power switch No matter what state the Mac mini was in, I could control the power switch. I proceeded to deploy my solution onto the test bed of 16 Mac mini’s and things worked great, but the solution was left out of the final design to keep things simple.  If the machines proved too susceptible to power problems I would implement the servo solution at that time.

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7 thoughts on “Filling The Void

  1. Daniel

    Allthough I like mechanical solutions involving servos, why don’t you plug a ethernet module + an atmega module running some sort of HID Emulation into the USB port and program it so send the “poweroff” keypress on command. that should even work if the machine hangs.

  2. simbimbo Post author

    Thanks for the feedback Daniel. I’ll look into it next week. It definitely sounds easier to manage.

  3. marko

    Please let everyone know what manufacturer you used for the power splitter cable… lots of people would like to buy those :-)

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