Thanks for returning for Part Five of Tech Service Today's technical buyer's guide series called Size Matters - Especially When Choosing A Network Rack which explains why IT professionals must evaluate every dimension of a cabinet or rack before purchasing one. Far too often product choices are made based on only one or two rack dimensions, and the repercussions of such carelessness can be costly.

In the first four segments we offered tips for calculating your real Internal Height requirements for a new rack or enclosure, emphasized the importance of comparing the height of your building's pathways to the External Height of a cabinet or rack, explained that some manufacturers are still making racks with 23" and 24" rail widths to accommodate old telecom equipment, so you need verify your Internal Width requirements before making a final purchasing decision, and providing tips for choosing a rack-mount enclosure with the best External Width to accommodate the type of equipment and associated cables that will be housed in your cabinet.

Today we will explore the best practices for determining the ideal Internal Depth of a new cabinet that will best accommodate all your rack-mount equipment.

Part 5 - Internal Depth

When deciding which rack-mount enclosure to purchase, one of the most critical measurements is the Internal Depth.  Believe it or not, the method for determining your internal depth requirement is pretty simple.  Start with the depth of the deepest piece of equipment you plan to mount, then add 4" - 6" to account for the space that the cables connected to the front and back of that equipment will need.  Then find a cabinet with at least that much internal depth.

So if it's that easy, why does this segment continue on?  It is because many IT professionals confuse a cabinet's Internal Depth with the Maximum Mounting Depth - the latter being the distance between the front and rear sets of rails when they are set at the furthest points to the front and back of the cabinet.

To better illustrate this problem, consider this real-world example.  An IT Manager just purchased several new servers that are all 32-inches deep. He is now shopping for a new 42U server cabinet in which to mount them.  The first cabinet he looks at seems perfect because it has an external depth of 38" and an internal depth of 35".  Certainly 35-inches is deep enough to accommodate the 32-inch deep servers, right?

Surprisingly, the answer is often NO.  While the cabinet's internal dimensions confirm that the servers will physically fit inside, you also need to determine whether or not the rails will extend to the depth needed to mount the servers at all four corners. In the case of this cabinet, the manufacturer's maximum rail depth is listed as 29.4-inches - several inches shallower than the servers.  But this doesn't necessarily mean he can not use that server cabinet.

Most servers offer adjustable mounting brackets that allow a deep server to be mounted on rails whose depth is a bit shallower (meaning a couple of inches).  So if that's the case with the servers in this scenario, and if the IT Manager does not mind when a server protrudes out beyond the face of the mounting rails, and if the doors to the cabinet will still close after all the cables are connected, then he could use that server cabinet.

The underlying problem is that many cabinet and rack manufacturers do not list Maximum Mounting Depth among their product dimensions. Since the difference between the mounting depth and the internal depth can vary from 2"-12" from one manufacturer to another (and sometimes with two cabinets from the same manufacturer), and because there is no magic formula for determining the maximum rail depth based on other dimensions, it is imperative that you know what both of those dimensions are before ordering a cabinet. If the maximum rail depth is not listed on the specification sheet for a cabinet you are considering, then contact the manufacturer to get it.

Tech Tip #5 - Internal Depth

Here are today's tips for determining the ideal Internal Depth of a cabinet.

First, determine the depth of the deepest piece of equipment you plan to mount in your new cabinet.  Then add at least 4"-6" to that depth to account for the space needed for the cables that will connect to the front and rear of your rackmount equipment. This represents your minimum Internal Depth requirement from which you can determine if a cabinet will meet your needs.

Second, determine what the cabinet's Maximum Mounting Depth is and compare that to the depth of the front and rear mounting brackets on the deepest piece of equipment you plan to mount.  If the rails can not extend to the depth your deepest piece of equipment requires, search for a deeper cabinet.

Final tip of the day is for those IT professionals who have a variety of different servers they want to install in a single cabinet.  Due to the weight of most large servers, their manufacturers always explicitly state that they must be 4-point mounted in a 4-post rack or cabinet. This can present a problem when the depths of your servers vary so significantly that it is impossible to mount every server on the same set of front and rear rails. The solution is relatively simple. Ask your cabinet manufacturer to install a third set of mounting rails in your cabinet.

Check back on Monday for our sixth segment in this series, focusing on the External Depth of rack-mount enclosures and how to factor depth into your considerations when evaluating a new cabinet.

Are you planning an IT rollout project involving the installation of new hardware and/or racks to multiple sites?  Then download a free copy of TST's Best Practices for IT Rollout Projects.   

5

Need help installing, troubleshooting, testing, documenting, or replacing your network cabling?  Call Tech Service Today for on-site technical services anywhere in North America - often in 4-hours or less.

Just call (800) 973-2022 (option 1), or Email us at Service@TechServiceToday.com