NAND-based storage media for industry: how to choose the right product

Cactus Technologies offers NAND-based storage media developed exclusively for industry. The company distinguishes between three categories: commercial grade, OEM grade and industrial grade. We will tell you which category is suitable for which application.

NAND-based storage media have been on a roll for years. Unlike hard disk drives, they are resistant to shock and vibration due to their static design (i.e. their lack of mobile parts). Their downside is a limited amount of write/erase cycles. NAND-based storage media should be evaluated carefully before any purchase.

The consumer market sets the pace
The market for NAND-based storage media is clearly driven by the consumer market. Devices from smartphones to cameras and notebooks are equipped with NAND-based storage media, often referred to as flash drives. Storage devices for industrial applications only account for a minuscule part of the overall market. This, in turn, makes it difficult to find sufficiently reliable and robust storage media for industrial purposes. NAND-based media come in the following categories:

Consumer grade – high memory density, low price
Consumer-grade flash drives are primarily used in entertainment electronics. As mentioned before, they make up the largest part of the market for NAND-based storage media. Consumer-grade flash drives offer a large amount of storage capacity at an affordable price. To achieve this, they use the cheapest available NAND modules, which are currently TLC-NAND (triple-level cell). They give the flash drives a very high memory density.

But this comes at the price of lower endurance and data retention rates. For this reason, TLC media are rarely used in industry environments, as they are simply too short-lived and vulnerable to error. The follow-up expenses incurred as a result of field failures quickly exceed the money saved by choosing a device from the cheaper category.

As a pure industrial manufacturer, Cactus Technologies does not offer consumer-grade storage media. Its standards of endurance and robustness go far beyond those of its competitors’ products.

Commercial grade – entry-level industrial devices
Unlike consumer-grade products, the commercial-grade flash drives by Cactus Technologies are designed for industrial applications. They are equipped with MLC-NAND (multi-level cell) rather than TLC-NAND modules. MLC-NAND distinguish between two bits instead of three. This means that they only have four, not eight, possible states per cell. As a result, MLC-NAND have a longer read life cycle than TLC-NAND, making them much more durable.

When evaluating industrial storage media, the fixed BOM (bill of material) plays an important role. Different production batches of consumer-grade devices can have considerable differences both in terms of the NAND modules and the controller. This can cause compatibility issues if a storage medium needs to be replaced and tends to incur considerable follow-up expenses especially in industry. Cactus Technologies offers a fixed BOM for its commercial-grade storage units. This ensures that the units remain completely identical for at least two years (and for much longer in most cases). It guarantees compatibility even when creating a byte-to-byte image.

Besides the NANDs, the core of a NAND-based storage medium is its controller and firmware. Cactus Technologies uses sophisticated controllers and firmware to improve the reliability and endurance of its products. With clever controller functions such as wear levelling, it counteracts the technologically limited write/erase cycles and data fading. This makes NAND-based storage media suitable for industry applications.

Testing is another important aspect. Industrial manufacturers such as Cactus Technologies subject their storage media to an extensive performance test prior to delivery. This effectively prevents premature field failure.

Industrial grade – unparalleled quality for the long term
The industrial-grade storage media by Cactus Technologies have considerably more write/erase cycles than their commercial-grade counterparts. Like the commercial-grade units, industrial-grade storage media are equipped with clever controller functions and a fixed BOM. Their high-quality SLC-NAND give them a considerably longer service life.

SLC-NAND modules only have two possible states per cell. This massively increases the endurance of the storage units: they have up to 30 times more write/erase cycles than MLC-NAND. Cactus also uses the largest available shrinks. This means that its storage media have a relatively thick oxide layer, so its NAND cells age more slowly than those of units with small shrinks.

The SLC storage media by Cactus Technologies are among the most long-lived NAND-based units on the market. They are used whenever particularly high requirements must be met: in medical technology, the rail and transport industry and other sophisticated industry applications.

SLC-NAND are also considerably less sensitive to extreme temperatures than MLC-NAND. Cactus uses SLC-NAND that were developed specifically for the expanded temperature range (–45 to +90 degrees Celsius). While there are MLC-NAND that are designed for this temperature range, they are only screened.

Another advantage of SLC flash drives over their MLC and TLC counterparts are their significantly longer product lifecycles. Cactus offers at least eight years of lifecycle management. The best example for the long availability of Cactus products is the 203 series, which has been on the market with only minimal changes since 2005.

OEM grade (original equipment manufacturer) – the best of MLC
SLC-based storage media are unparalleled when it comes to write/erase cycles. They can perform up to 30 times more write/erase cycles than MLC-based units. Especially with large storage capacities, this comes at a price.

pSLC storage media are a viable compromise between expensive SLC units and MLC units. The acronym stands for ‘pseudo single-level cell’. Cactus Technologies sells pSLC devices in its OEM-grade product range.

The pSLC technology is based on MLC-NAND (multi-level cell), but the NAND cells are used like an SLC storage unit. Instead of the two bits of MLC modules, pSLC modules only store one bit per NAND cell. The differences in voltage states are considerably larger than those in normally operated MLC-NAND. This gives pSLC storage units six times more write/erase cycles than regular MLC units. pSLC storage media offer solid performance at a reasonable price and are especially suitable for large storage capacities.

Which flash technology is suitable for which application?
For all applications that rely on a long service life and do not require more than 16 GB of storage capacity, we recommend investing in industrial-grade SLC storage media. This investment also pays off for applications involving high thermal stress, as SLC units are considerably more reliable in extreme temperatures than their MLC counterparts.

For industrial applications that require a lot of storage capacity, good endurance and functional reliability, OEM-grade pSLC units can constitute an attractive alternative. The belief that pSLC is equivalent to SLC is mistaken, however. The endurance of real SLC modules is up to five times higher than that of pSLC modules.

For a long time, commercial-grade MLC storage media used to be highly unpopular for industry applications. Today, some manufacturers use clever firmware to improve the endurance and reliability of MLC flash units. Nonetheless, MLC-NAND have thirty times fewer write/erase cycles than SLC units. We only recommend MLC for applications that do not crucially rely on long endurance, require extremely large storage capacities or only need limited write/erase cycles.

If you do choose an MLC unit, we recommend that you buy from a manufacturer with industry experience. Depending on the NAND shrink, controller and firmware, there can be vast differences between individual MLC storage media. The service life of MLC units can be extended by using large storage capacities. This distributes the write/erase cycles across more NAND cells.

The vast majority of TLC and new 3D-NAND storage media (consumer grade) are unsuitable for industrial applications. Their extremely high storage density impacts negatively on their endurance and reliability.