#datacenterfu

If you have a cabinet of servers to rack up, then you are going to have a lot of cables.

There's power, and probably several network cables going into each and every server. The other end of the cables have to go somewhere, so you're going to have cables coming back together in bunches at switches and power distribution bars.

You could have a couple of hundred cables in total in a full cabinet - and that's a lot. If you take a look below your work desk you'll almost certainly find a mess of twisted cables that are all intertangled, and that's a scenario where you've got no more than a dozen or so cables to deal with.

When you're commissioning a new cabinet of servers you are going to need a strategy to avoid a twisted mess of cabling. If you don't tackle this then you leave yourself open to several problems. Firstly, you (or more likely a remote-hands engineer) will find it difficult to trace a cable in an emergency, and secondly, you're going to impede the smooth flow of air out the back of your cabinet. Heat is your enemy in a DC, and you should do everything you can to prevent it building up - so you need to tie all your cables away to the sides.

You're probably by now thinking that you know what the answer is to the problem. You're thinking plastic cable ties, aren't you?

Well, those will do the job, but they are not the best solution. Plastic cable ties are great at holding bundles of cables together, but they are a pain if you later realise that you missed a cable from the bundle, or worse that you need to remove a cable from the bundle. They also create mess - if you chop off the end of the tie once it's in place, you'll soon find you have a lot of plastic bits to dispose of, and most likely they are scattered inside the base of your cabinet where they are hard to reach.

A better solution is to buy a long reel of double sided velcro tape. This is easy to get ahold of - just Google for something like "velcro cable roll".

Some providers sell specially pre-cut products that are the velcro version of a traditional plastic cable tie. With these you pull the end of the velcro tie through a hole in the other end of the tie to create a loop, and then stick the cable to itself. I suggest you don't buy this product. It is a faf, and you'll waste time trying to use it.

Instead, I suggest you splash out on a 10m continuous reel that has a cross-section that is around 18mm wide, along with a good pair of scissors which you'll use to cut the roll into suitable lengths.

Other widths are available, but I find 18mm to be about right - it is still possible to thread it through the square rack-mount holes in your cabinet to provide an anchor (although it is a tight fit). I also find that if you go for a tape with a smaller width - e.g. 10mm, you'll find that your anchored cables sag as the velcro fabric will bend, and also that it is more difficult to obtain a secure fit as the fabric has to be closely aligned to wrap around itself. Buy 18mm wide fabric, and none of these are an issue any longer.

The great thing about buying a 10m roll of double-sided velcro is that you are free to cut it to just the right length for each bundle of cables that you want to tie together. 

In addition there is no mess, and if you need to extract a cable from a tied bundle, you just unfasten the velcro from itself, and then reattach afterwards.

I find that when I'm commissioning a new cabinet, I'll typically use somewhere between 5m-10m of velcro cable tie, to make a good job of things. So buy a 10m roll - if you have some left you can use it to sort out that mess under your work desk!

This is a posting about computer power supplies.

Yes! PSUs!

Ok, so PSUs are dull as dishwater, but please allow me a couple of minutes of your time to explain how getting PSUs right in your Data Center can earn you #datacenterfu points and save your employer money.

The problem with PSUs isn't their reliability. I don't recommend buying servers with dual PSUs, but that is a story for another day. These days if you buy a server, you can be reasonably confident that you won't see the PSU fail during the whole lifetime of the hardware. No - the problem with PSUs is heat.

Put your hand over the grille at the back of a server PSU. Chances are you'll feel a fair amount of heat being pushed out through the little fan. Some of that heat might be coming from your disks or your CPUs - that depends on the physical shape of your server, but very often the heat is coming from the PSU itself.

PSUs are not very efficient in their use of electricity. A run-of-the-mill low-end server will come with a cheap PSU, which may only be 70% efficient.

Where does the other 30% go?

Heat.

This is bad for lots of reasons.

For starters, a rack full of 70% efficiency PSUs produce a lot of waste heat. 30% of the electricity they consume is going straight out the back of your servers as heat. That might be useful if you are a bedroom hoster who could do with a little help to reduce their heating bills, but in a DC heat is your enemy.

A cabinet full of inefficient PSUs could easily raise the exit temperature of your cabinet by 10C. That's a lot. The heat will start to soak through everything in your cabinet, and from my own experience, hot servers suffer more hardware failures than cool ones. Broken hardware is typically expensive to replace, particularly once you factor in paying for your visit to fit it and any revenue lost due to your outage.

Then you have to think about all that wasted electricity. 30% is a big number, and if you pay your DC for the actual kWh or kVA that you use, then you may be paying up to a third more than you have to. That could be a lot of money over the life of your servers.

There is another hidden gem in there that you might not have noticed. If you can somehow eliminate that 30% wasted electricity then you suddenly have spare electrical capacity in your cabinets that you can make use of! And remember - it is usually electrical capacity you are short of in a cabinet, not physical capacity. Eliminate the wasted electricity, and you can run additional servers in the same cabinet space reducing the total number of cabinets you need, and saving you even more money.

So the big question: Can you eliminate the extra heat and wasted electricity that your inefficient PSUs are causing you?

Not entirely, however you can make a huge difference.

I use Supermicro for my servers, and they offer a number of different PSU options for each of their chassis. Supermicro have had all of their recent PSUs tested, and given an efficiency rating. You can see at a glance which PSU is going to produce the least heat.

Of course, you can't make a device like this 100% efficient, but Supermicro do a great job, as they've got a number of units that are around 94 or even 95% efficient. 

Here is a useful #datacenterfu tip for you - sometimes it pays to purchase a PSU that can output significantly more watts of power than you need, to get the most efficient PSU for your chassis.

Consider this: Let's say you need a 300W PSU, but the 300W model is only 80% efficient. There is also a 600W PSU, and that model has 95% efficiency. The 600W PSU costs you an extra $50 to buy. Your server won't consume any extra electricity with the more powerful PSU (The excess wattage capability is all kept in reserve), in fact your PSU consumes less electricity, as it is much more efficient. Over 5 years you save much more than the $50 additional upfront cost on your electricity bills.

So - if your vendor has options on PSUs - and most will, as they like to cater for different wattage outputs - then take a look and see which the most efficient model is.

Buy that model, and your cabinet will run cooler, fewer servers will suffer hardware failures, and if you pay for the electricity you use, your bills will be considerably lower over the lifetime of your cabinet.

In a typical cabinet that I commission, there are a lot of different cables.

Every device has a power cable, and then there is the small matter of three separate network cables to each server. The switches all have a console cable, and there are fibre uplinks to contend with too.

That is a lot of cabling, and if you need to trace something it can be pretty difficult to see the wood from the trees. But if you apply a little #datacenterfu, you can make your life a lot easier.

If you've worked with servers for any length of time, then at some point I can guarantee you'll have come across the following scenario:

For one reason or another you need to trace a network cable within a cabinet from a switch to a server or vice versa. There are many reason why you might need to do this, and the reason isn't important. What's important is that the engineer who installed the cabinet didn't label any of the network cables, and now you are stuck trying to trace two meters (more if you are unlucky) of cable through tight spaces and a myriad of other identical, tangled cables.

It's a nightmare - and what's more you'll almost certainly be undertaking all of this under a lot of pressure because something in your system has broken, and people are shouting at you to get it fixed.

It doesn't have to be like this.

Like most other aspects of cabinet installation, applying a little #datacenterfu to the process will make a world of difference.