Feature: Embedded
applications with space limitations. If supported, NVMe technology can allow up to 10x faster read times of M.2 SATA devices, due to the use of the more- efficient PCIe bus, but this technology does not have the more comprehensive boot support that SATA drives offer.
Flash technology Te flash or NAND types dictate the speed and reliability parameters, but it’s not just a case of choosing the fastest and most reliable. Not only are these two maximums not available in the same NAND type, but the NAND type you’re able to use is dependent on the amount and frequency of data being written to and read from the SSD; see Table 1. Te acronyms SLC (Single-Level Cell),
MLC (Multi-Level Cell) and TLC (Triple- Level Cell) refer to the storage capacity for each type of SSD NAND Flash: the more levels, the higher the storage capacity, with TLC providing the most. TLC SSDs are also generally the cheapest, but, with increased storage capacity comes decreased reliability. Table 1 shows two other specifications
of Flash which fall between MLC and TLC. Tese 3D variants were introduced to patch the gap between storage increase and reliability, by increasing the number of electrons per bit of data. 3D TLC, for instance, boasts larger cell sizes than traditional TLC, yet allows it to meet, or even exceed, the MLC specification in terms of endurance and data retention. So, storage capacity is dictated by the
number of levels in the SSD Flash cell and is governed by the reliability one needs for a project. For critical applications, as an example, it would be pertinent to opt for a more expensive single-level cell, which trades storage capacity for reliability. For less critical applications, multi- or triple- layer cells are just fine, which provide far more storage capacity at lower cost and reliability.
Environmental factors Environmental factors are just as important. Tere is a general rule of
Table 1: NAND technologies
thumb as to what is considered “normal” temperature, which falls somewhere between 0°C and +50°C, with devices sitting in environments that fall outside that range generally requiring wide or extended temperature capabilities. And it’s not just the ambient air temperature that needs to be factored into the calculations — in scenarios such as devices in direct sunlight, the temperature inside the actual enclosure will ramp up due to heat exchange from the other components — these are all environmental aspects that need to be considered during the planning stage. Fortunately, many of the manufacturing
partners available from Impulse Embedded offer SSDs with wide temperature ranges, along with conformal coating, a varnish- style covering applied to components such as PCBs to protect from high humidity or moisture ingress. A full understanding of the end application will ensure the selection of most appropriate drive.
Power matters Finally, power source reliability to your SSD can make or break a project depending on the contingency in place at a hardware level. For example, recently, a customer wished to install multiple embedded PCs spread across a factory floor. During the planning stage, a 360-degree assessment identified that power fluctuations and dips caused by the general operation of heavy industrial
machinery on the same power ring could be so great that HMIs would switch off and PCs restart, causing risk of critical failure through improper shutdowns. To counter this risk, an SSDs with Power Guard was provided, which have additional capacitors on board to ensure that data writes to the disk are completed fully in the event of power loss, thus reducing the risk of corruption and data loss in this critical environment.
Planning and monitoring As with most situations, and practically all industrial and embedded computing applications, prevention is better than cure. Even with a component so common and seemingly innocuous as a storage device, the planning stage can ultimately make or break an entire industrial or embedded system. But, it doesn’t end there — ongoing monitoring is also required to maintain a stable and reliable system, with predictive maintenance systems and timely maintenance and replacements advisable. Most of the manufacturing partners in the Impulse Embedded portfolio offer soſtware to monitor the health of your SSDs in real time, sending email alerts to the customer’s support team should the SSD require attention. Tis kind of predictive maintenance and timely response in the event of a failure minimises or even eradicates downtime during critical times of operation.
www.electronicsworld.co.uk April 2021 23
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