Unmanned Systems Technology 009 | Ocean Aero Submaran S10 | Simulation and testing | Farnborough report | 3W-110xi b2 TS HFE FI | USVs | Data storage | Eurosatory/UGS 2016 report

70 Focus | Data storage unattractive. The cost per gigabyte of flash memory remains far higher than that of hard drives, and flash memory has a finite number of programme/erase (PE) cycles. A solid-state storage PE cycle is a sequence of events in which data is written to the NAND flash memory cell, then erased and new data rewritten, and these cycles can serve as a criterion for quantifying the endurance of a flash storage device. Flash memory devices are capable of only a limited number of PE cycles because each cycle causes a small amount of physical damage to the medium. This damage accumulates over time, eventually rendering the device unusable, and the number of cycles a given device can sustain before this occurs varies with the type of technology. The least reliable technology is called multi-level cell (MLC); enterprise-grade MLC (or E-MLC) offers an improvement over MLC, and the most reliable is known as single-level cell (SLC). There is some disagreement in the technical literature as to the maximum number of PE cycles each type of technology can execute while maintaining satisfactory performance. For MLC, the typical maximum PE cycles per block range from 1500 to 10,000. For E-MLC they can be up to about 30,000, while SLC devices can execute up to 100,000. In addition, deleted files on all SSDs can remain there for an indefinite period of time before being overwritten by fresh data; erasure or shred techniques or software that work well on magnetic hard drives have no effect on SSDs, compromising their security. An important goal of NAND flash development has been to reduce the cost per bit and increase maximum chip capacity so that flash memory can compete with magnetic storage devices. However, as one manufacturer of flash memory points out, “If you try to cram several layers of memory into the same space that a single layer would normally take up, the complexity becomes higher; the flash has greater capacity but there are more chances for errors, so reliability and speed may drop a little.” The choice between the two general types of NAND flash, SLC and MLC, depends largely on the application. If the drive is to be used for booting an operating system or maintaining a system then SLC NAND is very popular. However, for large-scale or high-speed data recording then, as a rule, an MLC solution is more cost-effective. Even in its worst condition, in terms of the loss of memory capacity due to the PE cycles, an MLC drive will function for several thousand overwrites, after which it can be replaced, which is more cost- effective than buying a high-capacity SLC drive at the onset of a project. That ability to replace drives has led to it being supplied in removable canisters or data cartridges. As the technology becomes more memory-dense, and the physical dimensions of the NAND flash become narrower, the overall PE cycle per cell primarily in the MLC market is much less than with previous technologies. However, a new flash technology called 3D NAND has arrived recently on the market. 3D NAND allows older technology to be stacked to give greater capacity while still maintaining better PE cycles. This will improve the reliability of the next generation of NAND flash, and some top-end systems are already using the technology. 3D NAND is suitable for the August/September 2016 | Unmanned Systems Technology Solid-state drives are being deployed in a wide variety of computing platforms due to their durability, boot-up time, application performance, responsiveness and power savings (Courtesy of Soligen) Stacked solid-state drives are available in capacities from 32 Gbytes to 5 Tbytes (Courtesy of Soligen)