By Matt Lundberg, Technical Lead, Industrial IoT, Impulse Embedded
Choosing the correct Solid State Drive (SSD) for your industrial computing or embedded system application is key to maintaining a successful, reliable installation. Industrial and embedded computing applications are as varied as they are complex, but fortunately this variation is also reflected in the multitude of SSDs available on the market.
With various form factors, durability and security features, the selection does not always boil down to price, and choosing which SSD is right for your single board computer or fanless PC can mean the difference between an installation truly fit-for-purpose, or one with the potential to under deliver, or worse, fail completely.
Form factor defines features
Form factor is perhaps the first consideration when choosing an SSD for an industrial or embedded computing application. It’s not just about space; with different form factors come different interfaces, and different interfaces provide various features that may or may not be applicable to your industrial or embedded computing installation.
For instance, if we look at the 2.5” SSD, which is arguably the most commonly available in ready-to-go integrated embedded computers, this offers a number of benefits: due to its ubiquitousness, availability is never normally an issue, and these large-capacity drives are easy to install. They support most (or even all) flash technologies, such as TLC, MLC and SLD, often support extended temperature ranges from -40°C to +85°C, and provide options for resilience technologies, which protect your data and operating system from power instability or outages.
If you would prefer your SSD to be installed using a more discreet method, perhaps in an effort to reduce overall system footprint, or are using an embedded computer board with a single power source, then MSATA or M.2 (MSATA’s updated equivalent) could be the best option. These drives fit parallel with the board, taking their power directly from the SBC/embedded PC, whereas 2.5” SSDs require separate cabling for data and power, which take up valuable room in embedded applications with space limitations. If supported, NVMe technology can allow for up to 10x faster read times of M.2 SATA devices, due to their use of the more efficient PCIe bus, but this technology does not have the more comprehensive boot support that SATA drives can offer.
The flash, or NAND, type dictates 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.
(Program Erase Cycles)
|SLC||Stores 1 bit per cell and 2 levels of charge||50000 – 100000|
|3D MLC||Stores 2 bits per cell 4 levels of charge||20000 – 30000|
|MLC||Stores 2 bits per cell 4 levels of charge||1500 – 3000|
|3D TLC||Stores 3 bits per cell and 8 levels of charge||500 – 3000|
|TLC||Stores 3 bits per cell and 8 levels of charge||300 – 1000|
Table 1: NAND technologies
The acronyms SLC (Single-Level Cell), MLC (Multi-Level Cell) and TLC (Triple-Level Cell), dictate the storage capacity for each type of SSD NAND Flash: the more levels, the higher the storage capacity, with Triple-Level Cells (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. These 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 provides far more storage capacity at the potential cost of lower reliability.
Environmental factors are just as important. There is a general rule of thumb as to what is considered “normal” temperature, which falls somewhere in 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 other components — these are all environmental aspects which need to be thought about during the planning stage.
Fortunately, many of the manufacturing partners available from Impulse Embedded offer SSDs with these wide temperature capabilities, 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 the most appropriate drive.
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, a customer in 2020 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 would 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 software to monitor the health of your SSDs in real time, sending email alerts to the customer’s support team should the SSD require attention. This kind of predictive maintenance and timely response in the event of a failure minimises or even eradicates downtime during critical times of operation.