As we learned earlier in this article, good housekeeping practices such as how best to plan and organize your network cabling are important for keeping your server rooms and datacenters functioning well. But proper feeding and care of your racks and cabinets is also an essential part of that discipline, and that is what this article is all about. So once again I’m going to share some tips I’ve learned over the years from visiting datacenters and talking with IT pros who design and administer them. And as with planning and implementing wiring in a server room or datacenter, best practices for selecting and deploying the right racks and cabinets is also something that is often learned from trial and error after finding out that initial choices and solutions don’t meet your expectations.
One IT pro who has learned a lot about this over the years is Ken Chase the founder of Heavy Computing Inc. in Toronto, Canada, and he has some helpful thoughts on these matters which he shared a while back with a group of network operators and which he has given me permission to share here with our TechGenix readers. Ken founded Heavy Computing 11 years ago after starting out in the early Internet industry in the mid-1990s and he has been providing clients with datacenter and processing solutions that range from wiring and cooling plans to hardware procurement and deployment, management and operations, and user experience design. Ken currently services a boutique set of clientele in custom-run datacenters in the greater Toronto area and I’ve included some excerpts from the comments he shared in the sections below to pass on some of his hard-earned wisdom to our readers.
Know your budget
If the budget is in the millions of dollars then you can afford to go all-in with purchasing your racks and cabinets from a single vendor. Full-rack solutions that come with extendable arms for customizing how you arrange your servers, switches and other networking hardware are terrific if you can afford them. But they are also both expensive and vendor-specific in their design so if you decide and can afford to go that way you basically need to buy everything from a single vendor. But as Ken says, such an approach is “not practical for varied species installed over longer periods” so if you can afford to purchase everything up front and don’t plan on later incremental expansion of your datacenter then this is probably the way you should go.
Watch for vendor compatibility issues
If your budget is more limited and you expect to grow your rack and cabinet infrastructure over time, you still need to be aware of issues with compatibility between different vendors of infrastructure hardware. For example, as simple a matter as whether servers are powered from the left side or the right varies between different vendors, with IBM and Dell on one side and HP and Sun Microsystems on the other. Ken’s response to this kind of vendor behavior is refreshingly vocal: “Curse vendors for not picking a standard side for power ingress!”
Choose the right size cabinets
If your cabinets won’t have any side panels or have any neighbors, then it’s probably all right to use 24x30-inch cabinets in your server room. But generally speaking, it’s best if you go for cabinets that are 30 inches wide and 36 inches long as Ken says this “make all the difference” since you can position your cable wrangling ladders on one side of the cabinet and your 0U power distribution units (PDUs) for A/B redundant power for your servers on the other side of the cabinet. Ken adds that cabinets that are 36 inches deep also “allow facing the PDUs backward, not sideways, i.e. cable heads extend backward, not into the rail-tail path or airflow.”
Favor cage nuts over screws
Ken says flat out to “avoid racks that don’t use cage nuts” and have pre-threaded holes for rack screws. The reason is simple: “Pre-threaded holes get abused and stripped.” Watch out also for the kinds of cage nuts you buy as there are several different sizes available and some of those sizes may fit poorly on your rack or cabinet. And as we’ll see later in this article, poorly fitting cage nuts can lead to painful accidents if you’re not careful when installing them.
PDU installation tips
Ken also shares several hard-earned tips concerning installing PDUs and networking hardware in cabinets. First, he says he “offsets his PDUs vertically by half a plug-spacing distance as it allows the cable from the left one to fit between the cable heads of the right one.” Then for those whose cabinets are limited in space, he suggests that it’s “worth getting the 90-degree bent-head cables too if you need the spare inches.” Ken also laments why power cables are often either too short or too long for proper installation of servers and switches in cabinets. “Not having zip-tied loops of 12-gauge wire hanging around makes things much nicer” in how they look, but more importantly it also “makes better airflow,” Ken says. So where possible try to mix and match power cables of different lengths so you can avoid having bundles of cables interfering with the cooling system in your cabinet.
When you first get your hands on your rack, it’s also a good idea to start off by pre-wiring any gear you’re going to mount in the rack that needs to be powered from the front instead of the back. Ken takes a careful preplanned approach on this matter, and usually has “five pairs (A/B) going to the front permanently zip-tied and labeled, with 3x2 in use for back-facing switches, one for small pieces of gear, and others as spares.” Ken also suggests pre-wiring as much of your Ethernet cabling as you can since fishing Ethernet cabling through the side afterward “can be impossible in a full cabinet in a dense row” as is often the case in an overcrowded server room or budget-constrained datacenter. As a tip, Ken also suggests to “leave some string in there too” so you can pull more cabling in afterward if necessary, and possibly more string as well.
Keep safety in mind when configuring racks and cabinets
Finally, always keep safety in mind as you install and configure racks and cabinets in your server room or datacenter. Whenever you deal with equipment like this there is the potential for danger, both of the mechanical and electrical varieties. For example, you should watch out for certain special features that vendors include in the design of their products to differentiate them from those of other vendors. The long fins or tails on the end of the rails of Dell’s racks are a good example of this as they may not fit properly into your 30-inch cabinet, depending on how the vertical mounting rails have been placed and the power cord head has been positioned in the cabinet. Ken, for instance, shares a story of how he saw an administrator “jam a long Dell rail’s tail into his fully assigned cabinet in between a power cable head and the power distribution unit it was plugged into.” The result? “BZZT! Took 20 minutes to get a monkey to reset at central panel.” As Ken says, "Thank goodness for proper cabinet grounding cables!"
But electrical shock isn’t the only hazard you may face when you setting up or reconfiguring your racks and cabinets. For example, if your rack screw or cage nut doesn’t fit properly you might try to force it in using a screwdriver. This is not a good idea however as Ken says he has “seen people stab themselves in the hand” when trying to do this. Ken’s suggestion in this regard is worth remembering: “Ask for a cage nut tool, a J-hooked shaped piece of metal that looks like a bent desktop-case PCI slot cover.” Using the right tool for the job not only makes your work more efficient, it can also save you from a trip to the hospital or clinic to get stitches. And who likes visiting the hospital?
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