Low-level data storage

The rising pressure on price in all markets — including industrial and embedded — has caused many storage solution manufacturers to resort to cheaper multi-level cell (MLC) and three-level cell (TLC) NAND flash memory technology. However, some users are taking the opposite route and are using single-level cell (SLC); especially in smaller and medium-sized form factors that require less than 32GB of storage capacity.

The decision as to whether an MLC memory solution is sufficient or an SLC is needed is not a simple one to make, because there are many factors that play a role. In principle, two profiles can be distinguished; the first is ‘extreme data retention’ applications, in which data is primarily read and hardly ever written. The other is ‘high endurance’ applications, which involve high numbers of write operations and are used, for example, in video surveillance cameras.

An example of an ‘extreme data retention’ application is the car navigation system. Theoretically, map data is only written once to the SD Memory Card, and is thereafter only read. It’s a similar scenario with solid-state drives (SSDs) used solely as a boot drive or recovery drive, for example in ATMs. In these cases, MLCs with their lower ‘write endurance’ are often quite sufficient. However, there are other practical factors that will have an effect; applications in vehicles will often involve exposure to very high temperatures, which impairs data retention times considerably.

If a device is expected to retain data reliably at high temperatures for years, this can only be achieved with special data refresh methods, which the firmware executes using clever analysis techniques. Such applications will often require the use of SLC NAND, as the refresh algorithms also strain endurance. This is especially the case when the application does not solely involve read operations and is part of a system that has not been rendered uninterruptable, in which case the memory needs to exhibit excellent behaviour in the event of a power failure. This is the case in 99% of all applications in which safety and security are factors, for example in transport, medicine, communications networks, industrial computers and, also, in automation.

Taking control of your data

Whether an MLC storage solution is sufficient also depends on storage density, controller technology, and firmware algorithms. With larger form factors, such as 2.5in SATA SSDs with storage densities exceeding 64GB, high-quality MLC NAND flash will also often satisfy requirements, as the degradation of memory cells can be spread over a large area. However, it is recommended that the load of the SSD always be verified. S.M.A.R.T. values and design-in service from Swissbit make it possible to calculate the expected service life of the SSD in use.

For lower storage densities and smaller form factors however, an MLC solution is usually not sufficient. In these cases, data needs to be spread over a smaller area and it is not possible to utilise controllers that are as large or powerful, thus reducing service life considerably. This usually necessitates the use of SLC NAND flash; especially since the quality of MLC NAND flash has declined constantly in recent years.

The new MLC generations no longer achieve the same levels of reliability as the older ones. After all, cost pressure affects not only application manufacturers, but also storage solution manufacturers. Swissbit has found that many customers are now stricter with their specifications and demand memory quality matching the second-to-last generation or SLC solutions, because they have had some bad experiences with current MLC solutions.

For them though, it is proving increasingly difficult to acquire high-quality storage solutions, because the mass market is trending away from SLC to MLC and TLC flash technologies.

A shortage of storage

In terms of overall market share, TLC currently holds around 60-75%, MLC 20-35%, and SLC 3-5%. This is making SLC and increasingly MLC — especially in industrial-purpose quality — a niche product. Accordingly, an increasing number of suppliers, including recently Western Digital, have abandoned the industrial market and are exclusively concentrating on server and client applications. The embedded market is too heavily fragmented for them, making it too costly to serve.

In the field of 2.5in SSDs, providers often don’t assume a clear market position, making it difficult for customers to determine who is an industrial supplier and who isn’t. It’s not only dependent on the quality of the products themselves, but also on whether their long term availability is secured, whether a fixed bill of material (BOM) exists, and whether there is a stringent PCN process.

At present, Swissbit is the only memory expert and manufacturer of memory products in Europe that has an explicit long-term focus on the industrial and embedded markets. Around the world, there are a few suppliers from the USA and from Asia, but none offer such a flexible and customer-focused industrial range. In order to produce the much lower quantities with often specific and higher requirements at marketable prices, Swissbit has been employing a flexible system of in-house production in Germany for years. This comprises considerable investments in a technical consulting team and in a planning tool that ensures efficient management with extended quality management and improved quality assurance.

Cost-sensitive solutions

In addition to the wide SLC portfolio, Swissbit also offers interesting solutions positioned between SLC and standard MLC for cost-sensitive applications. Using specially tested and selected MLC flash raw materials, the EM-MLC (endurance managed multi-level cell) model of the 2.5in SATA SSD X-500 series achieves endurance levels that are three to ten times higher than with conventional MLC, while maintaining the same data retention. EM-MLC memory offers extremely attractive performance relative to price (cost per gigabyte) and very high data reliability. This makes it the ideal solution for cost-sensitive industrial applications that don’t use a large number of write operations but still have increased requirements, for example a larger temperature range, high resistance to shock and vibrations, and transparent diagnosis functionality.

An additional innovative solution is an MLC that is operated in ‘reliable mode’. It offers ten times the write endurance, while only doubling the cost. This is currently available from Swissbit on a project basis.

Regardless of whether a customer selects an SLC solution or one of the relatively new MLC models, with Swissbit they are always on the safe side when it comes to quality and a low TCO (total cost of ownership). For this, only high-quality, industrial-grade materials and semi-finished products are selected, which are further subjected to stringent quality checks and processes using state-of-the-art production methods. Clever firmware and NAND flash management algorithms ensure maximum security and reliability, while long-term availability and established PCN processes are a matter of course for an industrial supplier.