A network attached storage (NAS) unit is a computer appliance used solely for data access and backup. A conventional NAS is usually a relatively large, multiple-drive machine located in a cooled computer room, providing shared data access and storage to all or most of the users of a networked system.
Because these appliances are situated in air-conditioned control rooms, the performance criteria for the storage drives are concerned less with environmental durability and resiliency than with access speeds and mean time before failure. Yet with today’s increasingly mobile information technology, there is a rapidly developing market and growing need for an industrial quality NAS that may be widely used in mobile applications or at remote field sites where environmental factors are unusually harsh and severe. NAS units are, for example, used on transportation vehicles such as buses, railcars and other rolling stock, while others are being used in power stations where heat, vibration and overall reliability are a great concern. For these applications, conventional, commercial NAS designs simply cannot withstand the environmental stresses; these designs require upgrading to industrial standards that can accommodate the harsh effects these demanding environments inflict.
To be a rugged NAS there are several challenges that need to be addressed from the very outset of the design and development process. Chief among these are vibration and shock tolerance, hardiness in extreme temperatures, both redundant power supply and redundant network connectivity and water and dust resistance.
Vibration and shock
The first challenge for a rugged NAS device is the vibration issue, because this is a particularly significant problem when it is used on a railway, bus or other moving vehicle. Consequently, in these environments suitable NAS solutions must meet or surpass the vibration standards defined in EN 50155 and IEC 61373, requiring careful design of both hardware and software.
Properly designed hardware must have a high resistance to damage from the constant vibration and shocks that occur on moving vehicles. This means that engineers must carefully select and test components and PCB designs even before the final shape of the device internals has taken a definite form. More importantly, because one of the fundamental requirements of any NAS is a large and reliable storage capacity, the hard disks used must be both high-performance and high-capacity, while also resisting industrial grade shocks and vibration.
Meanwhile, the appliance must also feature software utilities that will supplement the hardware priorities by actively adjusting the system to protect the storage drives from extreme circumstances. For example, when vibration or shock levels exceed specified measurements, the drives must be capable of protecting the physical disk (if disk drives are being used) by automatically shutting down all data access processes. In such an event, a properly industrial grade NAS will temporarily store all data in a suitably large, non-volatile buffer memory and then automatically write this data to disk once the vibration or shock reduces. For this, an independent vibration/shock sensor more sensitive than a hard disk’s internal sensor should be used to initialise vibration protection processes before environmental extremes have the chance to affect the disk. This requires sophisticated and detailed software design.
Temperature
Another problem is severe temperature, both at the high and low extreme. A NAS unit mounted on a vehicle, or in a harsh, remote industrial environment like a power substation or wind farm, will need to endure temperatures a commercial system simply cannot tolerate.
To keep a NAS operating in extreme heat, engineers must select components that quickly and effectively dissipate heat, or, maintain system performance while generating much less heat than standard commercial components. Adding to this difficulty is the need for eliminating internal fans: fans break down easily and often and these events inevitably result in heat-sensitive components frying themselves. Ideally, industrial-grade devices should eliminate this point of failure wherever possible. Taken together, this means comprehensive thermal evaluation across all hardware arrays from component level up.
Guaranteeing system operations in extremely low temperatures is an equally difficult challenge. For climates where temperatures can drop to well below zero, an intelligent, on-board heating solution is necessary to warm the device to a temperature that allows the NAS to remain available to the network. Again, this means a sophisticated design combination of an onboard heater with intelligent software controls.
Finally, a properly resilient, industrial-grade NAS should be equipped with the ultimate failsafe: a temperature sensor that will halt disk operations when thermal limits are exceeded and resume disk accesses when the system returns to a normal operating temperature. This method is similar to the vibration protections described above, except that in instances of such extremely high temperatures non-volatile memory is no longer an option. During this period the local network will lose access to its storage system, as if the NAS has gone offline. It is inconvenient, but when the system’s internal heat reaches limits greater than 70 or 80°C, a temporary shutdown is the only thing capable of reliably protecting the hardware from burning out.
Network and power redundancy with dual PoE+
Two other critical issues for any network service are data and power redundancy.
Network redundancy is simply achieved: equip the device with two Ethernet interfaces to guarantee that the network remains up should one fail.
Power redundancy, on the other hand, is not so common. Failure of a power input is so rare in control room NAS units that it has never been an issue. For commercial NAS appliances, an uninterruptible power supply (UPS) is really all that is needed. Yet on most vehicles and in many industrial environments space is tightly restricted, making a UPS not an option.
Once again, good, advanced engineering is capable of providing an efficient, cost-effective solution. By using Power over Ethernet Plus (PoE+), power redundancy is achieved using the same lines and interfaces as used to provide network redundancy. In addition, because PoE is somewhat restricted, the device will necessarily run on a relatively low power draw, reducing not only the cost of installation, but also reducing its overall cost of operation.
IP rating
Finally, as any industrial engineer knows, dust and water are ever-present concerns when building machines to run in industrial environments. Designing the machine to meet a suitable IP rating is thus another crucial factor when building a rugged NAS. IP54 is typically the minimal requirement for networked devices that must remain reliable despite exposure to the elements. An IP54 rating means the enclosure protects against dust, humidity and splashed water. NAS appliances which meet this standard can be depended upon to remain functional even when there are torrents of wind and rain raging just outside the hood.
Conclusion
With more and more industrial applications requiring NAS as part of their core systems, it is important to have a rugged NAS alternative that meets industrial requirements. To fulfil this need, a NAS properly described as industrial and rugged must conquer the challenges of vibration and shock, remain stable in both low and high temperatures, give reliable network and power redundancy (even in remote field sites), and be resistant to dust, water and wind.
Moxa’s RNAS-1200 series is just such a rugged NAS. The RNAS-1200 meets or exceeds the definition of ‘industrial grade in every way, making it suitable for industrial applications such as rolling stock, buses, power substations and remote automated facilities like wind farms. Equipped with Moxa’s Data XPro utility, the RNAS-1200 also comes with Moxa’s proprietary intelligent heating solution, an automatic cut-off for high temperature thresholds, and protection against vibration and shock that guarantees reliable access to data even in extreme conditions. The RNAS-1200’s sophisticated hardware and software design makes one of the most dependable, cost-effective storage appliances available for harsh industrial environments.
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