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What type of server rack/cabinet should I buy?

Over the years I have run into any number of problems physically mounting servers/equipment into racks/cabinets/enclosures.  This is often a major headache as it is not easy to change out your enclosure without taking everything offline, and often times (in the case of colocation facilities) it is simply not an option.

I was asked yesterday by a colocation facility for my advice on what types of new cabinets they should buy, which started me thinking.  I decided to post my current recommendations online in the hopes that it is of use to others:

  • Any server cabinet you buy absolutely 100% must have front to back cooling with fully perforated doors (none of this lexan crud with small holes and fans).  Every last square inch of the front and back needs to be perforated.  Period.
  • Don’t even think about using a bottom-to-top cooling setup cabinet.  If your colo provider tries to give you one of these, run away screaming.  This type of design was intended for telco style equipment.  What happens is the gear in the top of the rack bakes.  With modern gear you need much more airflow than that model can provide.
  • Make sure the cabinet is deep enough for everything you intend to put in it (including bezels on the front and cables on the back)  This is the largest problem I run into with colocation facility’s that have old racks.  The equipment has gotten longer but a lot of facilities don’t want to spend the money to upgrade (and the longer ones take up more floor space).  From a quick survey of rack manufacturers, it looks like 42″ is the new standard depth that should work with pretty much everything.
  • Make sure any cabinet you buy has standard mount points for vertical mount PDU’s (Power Distribution Units).  With density increasing vertical PDU’s are the only way to go (and they put the power strip right where you need it so you can use extremely short power cables).
  • The industry standard is now to have square holes rather than round holes.  This keeps you from stripping out threading and ruining an entire rack rail.  You can put cage nuts in the holes if you need threads.  (As a side note, I have seen at least three types of round hole racks, two with different types of threading, and one with no threading at all – I am glad these are all going away – except in two post racks where threaded holes are still standard)
  • Vertical wire management channels, chases, brackets, are a plus.  Think about how you are going to run your power, network, fiber, etc… cables.
  • Make sure the cabinet is built heavy-duty enough to handle the increased density of modern equipment.  Older cabinets were not designed for today’s weight loads.
  • The cabinets you get need to have proper heavy-duty bolt down points for earthquake and stability purposes (so they don’t tip over on you when you pull out servers).  Think about how this will work in the context of raised floors (if you have raised floors).
  • Decide if you want combo dials on the cabinets, or key’d entry.  I personally think colo facility’s should offer both and let the customer decide.
  • Your standard height cabinet is 42 rack units.  I don’t see any reason to deviate from this unless you can’t get something that tall into the building.  They also make taller ones, but who really thinks lifting servers above your head is a good idea OHSA wise?
  • Standard width these days is 24 inches.  If this is your own personal datacenter you could consider wider cabinets to provide a little more wiring space, but 24 is the industry norm (note that regardless of cabinet width, the rail width needs to be 19″ which is the standard).
  • Some cabinets come with split rear doors for reduced clearance which I find to be very convenient in many cases.  I really like the Dell ones.
  • The doors need to be very easy to remove and put back on (by ONE person) without hassle (like little nylon washers that fall out and get lost).  The doors should not bow or flex such that lining up the pins is a pain in the butt.  Dell gets good marks here too.
  • When you go to put equipment in your cabinet, if it has adjustable rails, make sure to adjust them properly BEFORE you install all your equipment.  Most server equipment can accept a certain range of depths these days so pick a depth that fits all your gear.

As usual, please post below if you have any comments/questions or shoot me an email!

-Eric

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  1. Thomas Gronke
    April 6th, 2010 at 09:17 | #1

    Any opinions on grounding? I don’t have hands-on commercial data center experience, but from previous experience in a corporate raised floor, I saw a variety of grounding methods, which included a mix of AC- and DC-powered equipment within racks.
    –A ground bus ran under the floor with individual ground wires run up from the bus and attached near the bottom of the rack.
    –Overhead metal cable management tray used as a ground bus, with individual ground wires between the top of each rack and the tray
    –None at all. This was common for roll-around cabinets that were landed on the raised floor, and depended on the grounding in the power distribution within the cabinet to attach to the electrical ground underfloor. These were typically used in server-only cabinets.

  2. April 6th, 2010 at 09:51 | #2

    In my 10 years of IT experience I have not run into any weird issues with x86 servers I could attribute to grounding problems. We are not dealing with analog audio equipment that suffers horribly from ground loop issues.

    I have seen some extremely expensive engineered grounding systems in the past, but I have never been able to prove the value of them by pointing to poorly grounded examples that caused problems.

    Every piece of IT equipment (well, just about) has a ground prong on it’s power cord which provides sufficient grounding (assuming the building/UPS wiring is correct). I recommend just grounding cabinets and cable trays as required by code and calling that good.

    I have not worked in DC power environments before so I am not sure if everything I have said above holds true.

    -Eric

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