Most Common Rack Computing Mistakes

Jake MacWhirter

Working for more than 15 years in the industrial computer hardware industry, I’ve seen many mistakes from rack integration projects. Luckily, they’re all easily avoidable with a little bit of guidance.

Here’s 10 of the most common mistakes or areas overlooked when developing custom-built integrated rack computers.

Airflow (obstructions to rear)

The number of rackmount computer platforms in the field that have vented doors and some form of obstruction to the rear is a concern. Typically, these cabinets appear to operate as they should, failures may be higher to an extent, but not dramatically.

However, deployments like this are in actuality rolling the dice, there is little or no understanding of how closely they are operating to a failure threshold. This increases risk and cumulative damage, therefore heightening the likelihood of failure due to elevated temperatures.

Within a densely populated rack mounted computer platform, many installers seem to bank on the fact that they have gotten away with it until now and therefore assume that all is as it should be. Only to later pull their hair out on the day it all goes wrong and everything seems to be falling over, exclaiming that they have no idea how this could have happened.

Pulling the cabinet away from the wall, though it may address a few of the immediate issues, is simply too little too late, many more potential failures now lie dormant only to present themselves over time.

Airflow – (plinth not open)

Many rack computer manufacturers provide attractive dress kits for the base of their products, some are vented and allow for airflow and some do not. If for example, there is a solid or glazed front door without an open floor tile and as such are reliant on the open base to the cabinet for sufficient airflow, fitting a dress kit (even a vented one), will close off the already limited air entry route. This will lead to increased failure rates, unpredictable reliability and an increased TCO due to additional parts and service calls.

Always assume the airflow must be open and then validate any items added to the build which have any potential to impact airflow.

Without sufficient cooling, the platform will not be thermally robust and reliable, even if it does appear to work initially.

Airflow – (insufficient exhaust)

Another common issue is the lack of exhaust fans in populated cabinets, these are typically standalone.

Even if high-flow doors are fitted front and rear, allowing a reasonable clearance at the rear, do not assume the cabinet does not require further cooling.

In reality, network switches and many devices do not follow the same flow patterns as the majority of servers and may not be capable of drawing cool air from the front of the rack.

As they operate, they may be siphoning air from inside the rack for cooling and so any warm air within the cabinet can be recirculated, elevating their temperature and increasing failure risks.

Even with high flow doors, it is advisable to assist the cooling of the rack with the use of exhaust fans at the top assuming there is no ducted cooling attached, which is unlikely with a high flow rear door.

The exhaust fans in this configuration, do not need to be capable of performing the entire exchange required to cool the cabinet.

However, they should be sufficient enough to provide, maintain and exchange air at a rate which prevents critical elements from exceeding their design parameters.

It is often possible to provide this with limited flow, as an area of low pressure adjacent to the fan will draw air constantly from the surrounding area which maintains an almost vertical chimney effect. This removes or reduces any localised recirculation issues.

Power – (external connectivity)

It is a common occurrence that systems are integrated and during the process the engineer then realises that either the power required is higher than the incoming supply cable is safe to carry, or there is little to no information available on the termination required for upstream connection.

Failing to understand or fully clarify the upstream connectivity and protection required can lead to dangerous and potentially costly mistakes.

Power – (lack of isolation or protection)

Within a computer cabinet it is important to be able to perform service and maintenance safely. In order to achieve this, confirm there is a quick and effective method of providing isolation from the incoming supply.

If using a UPS, remember that it can maintain an output in this situation and as such an ability to manage and isolate this output should be provided.

This could be in the form of using the RPO port of the UPS, safety e-stop circuits, physical disconnection or MCBs.

Power – (distribution connectivity)

Rack-mount computer chassis house a multitude of devices; these often have dissimilar supply requirements.

This can be as fundamental as differing AC or DC supply needs or as minor as requiring a different style of connector at the PDU to ensure connectivity.

The number of options for power distribution devices and connectivity can be truly overwhelming. But, what should be kept in mind is the current and potential future requirements of the devices specified.

These should be grouped together where requirements are the same to review what solutions are available to meet this need.

Remember, it is not uncommon to have to add specific distribution capabilities to a rack in order to manage rogue devices.

Do not expect it to be as simple as fitting one large PDU with numerous ports; rack integration is infrequently this convenient.

Power – (sufficient supply and effective budget)

With multiple devices within the rack cabinet and complex electrical wiring, oversights have the potential to lead to exceeding the safe operational current loading of cabling and distribution units.

Some devices protect against this, however many do not. Failure to adequately review the power requirements of each device and the providing structure can lead to costly and potentially hazardous results.

One of the common issues is the use of Euro or UK Spec IEC C13/14 cables for products being deployed for overseas operation. It is not safe to assume that because it has an automatic switching power supply, the cable supplied is suitable or certified for use in all regions.

A 1100W server may run from a 6A cable without issue at 230V; however it would require a 10A cable to operate safely when being used on 110V. In order to mitigate such issues many customers are now stipulating the use of globally certified cables, these are often referred to as TRI-Rated cables.

While these cables mitigate several issues, they would not, for example, prevent an integrator or operator installing 12 of these servers into a cabinet and connecting them to a single 16A or even 32A PDU.

Irrespective of the amount of power available upstream, it is critical to ensure each device receives power safely and the review extends to all cabling within the cabinet. This should include any internal or upstream protective devices.

Safety – (electrical safety and bonding)

A visual inspection will typically allow physical and mechanical safety issues to be identified, however it does not enable actual or potential electrical safety issues to become visible.

With so many manufacturers providing peripherals, cabinets and power distribution solutions, it can be difficult to keep track of electrical paths within the cabinet and how effectively the various elements are providing protection to users from potential electrical failures.

Irrespective of the manufacturer or quality of the hardware used, the integrator of a solution utilising multiple devices becomes responsible for the electrical safety or potential lack of if, should an issue arise.

Never underestimate the importance of safety, always ensure that prior to shipping a computer cabinet an electrical safety study has been confirmed in conjunction with appropriate testing to demonstrate electrical safety.

Additionally, ensure an appropriate report has been recorded and provided either with the cabinet or future reference.

Logistics – (delivery and maintenance)

A common issue with basic delivery logistics is as fundamental and simple as it comes.

This pertains to the rack arriving on site, surviving the rigours of transport either through custom packaging design or through fortune, only to be confronted by a doorframe it cannot fit through.

This leads to the removal of cabinet hardware if it is not already shipped that way, having to lay the computer cabinet down so that it can be maneuvered through the frame.

This would at least be a possibility with a 600mm wide rack. However, given that more cabinets are being built on the 800mm wide by 1200mm deep footprint, laying the cabinet down would not resolve this issue when faced with a traditional doorway.

Understanding logistics prior to agreeing the cabinet height and footprint is crucial to successful completion.

It is vital to understand the size and weight of the proposed solution. Ensure it can pass through the access route and that both the cabinet and floor are suitable for the finished weight and its path through the building to the end location.

Expansion and through life operation – (future proofing and support)

Future proofing, spares availability and free expansion slots in the rack for expansion are often overlooked in the rush to get a solution into the field, however issues invariably arise over time that require onsite resolutions.

It is often more efficient and cost effective to consider these from the outset and plan strategies accordingly.

Cabinets are often required to perform their function for many years and as such the ability to increase, upgrade or refresh hardware in the field is essential.

Careful initial planning can aid in the selection of products with a suitable lifespan. This also ensures that maintenance and support can be accommodated with minimal disruption once rack computer hardware is deployed.

 

To learn more about Captec’s rack services visit our rack integration page. For rack enclosures visit our 19″ rack cabinets page. Or to view our rack computers visit our rackmount computers web page.

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