Choosing the correct SSD for your application

Form factor is perhaps the first consideration when choosing an SSD for an industrial or embedded computing application. It’s not just about space — or the hole the SSD is going into — 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 form factor, 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 (more details on these technologies later), often support extended temperature from as low as -40°C to +85°C, and also 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 them using the more efficient PCIe bus, but this technology does not have the more comprehensive boot support that SATA drives can offer.

This is where things delve a little deeper. 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.

Let’s begin by looking at the NAND types themselves:
 

NAND Type	Description	Endurance (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

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. It’s as you imagine: the more levels, the higher the storage capacity, with Triple-Level Cells (TLC) providing the most. TLC SSDs are also generally the cheapest, but before we reach for our wallets in excitement, with increased storage capacity comes decreased reliability.

You’ll see from the table above, however, that there are 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, you may choose a multi or triple layer cell, which provides far more storage capacity at the potential cost of reliability. Our specialists can advise on this if you need more information.

Environmental factors are one of the last things to mention, but no less 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 of 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 — scenarios such as devices in direct sunlight, the temperature inside the actual enclosure ramping 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 our manufacturing partners 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 ingress. Our specialists can help facilitate this using our close partner relationships should you require.

Finally, power source reliability to your SSD can make or break your project depending on the contingency you have in place at a hardware level. For example, we had a customer in 2020 who wished to install multiple embedded PCs spread across a factory floor. During the planning stage, our 360 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 a risk of BSODs through improper shutdowns. To counter this risk, we provided SSDs with Power Guard, 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.

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 needed to maintain a stable and reliable system, with predictive maintenance systems and timely maintenance and replacements advisable. Most of our manufacturing partners offer software to monitor the health of your SSDs in real time, sending email alerts to your support team should the SSD require attention. This kind of predictive maintenance and timely response in the event of a failure, allows you to minimise or even eradicate downtime during critical times of operation.

Should you need any advice on SSD selection or maintenance, our Device Specialists are always on hand to answer any questions you may have. For more information give us a call on +44(0)1782 337 800, or click here to send us an enquiry and we'll get back to you ASAP.