SSD Form Factors: Viking Modular Solutions talk at Flash Memory Summit explodes the possibilities

Everyone “knows” what an SSD looks like. It looks just like an HDD, usually in a 2.5-inch form factor with a SATA connector. However, that’s not the only possible form factor, not by a long shot. Yesterday, at the Flash Memory Summit, Viking Modular Solution’s Flash Product Marketing Manager Steve Garceau stepped through a series of alternate form factors in a session on NAND Flash SSDs for embedded applications. I found his talk mind-expanding.

Historically, said Garceau, the embedded industry has relied on a very few SSD form factors for board-level SSDs. These existing, adapted form factors include Compact Flash (CF), which is commonly used in high-end digital cameras; embedded CF; and embedded USB. These form factors are all based on PC interface standards originally developed for external PC devices and they do not serve all embedded applications equally well. In fact, if there’s a maxim that doesn’t work across the huge, expansive space of embedded design, it’s “One size fits all.” One size definitely doesn’t fit all embedded applications when it comes to SSDs, processors, or pretty much anything else. The design space is just too big to settle on one or even a few SSD form factors.

Further, performance expectations for all embedded systems are hyperaccelerating. Where embedded systems once relied on 8-bit microcontrollers and 16-bit DSPs, now 32-bit RISC processors (perhaps several such processors) are now the norm rather than the exception and requirements for SSDs in these embedded systems are also expanding rapidly. Embedded applications need “more capacity, more [NAND Flash] channels, and better performance” said Garceau. Ideally, SSDs targeting embedded applications must offer one or more of the following: high performance, increased capacity, enhanced reliability (more ECC), advanced feature sets, easy accessibility, flexible deployment, and easy system scaling. These growing requirements drive SSD controller design and SSD controllers for embedded applications must look increasingly like the controllers used for PC-centric SSDs. Specifically, they must offer high-end SSD features such as automatic wear-leveling because the embedded developer will not be bothered to add such features to the software running on the host processor.

These rising performance and feature expectations have made 2.5-inch, encased SSDs increasingly popular in some embedded designs, but these metal-encased SSDs with (typically) SATA interfaces pose real problems for many, many embedded designs. They’re too big, physically, and they present cooling problems. Consequently, embedded developers are turning to a growing number of alternative SSD form factors for their designs. Garceau showed several offered by Viking Modular Solutions:

• SlimSATA. These SSDs are 70% smaller than 2.5-inch SSDs and are available in capacities to 120Gbytes now, 256Gbytes by the end of the year. They employ a standard SATA drive connector but are not encased and can be bolted to a host board. Transfer rates are 100-200 Mbytes/sec.
• The Cube SSD. This design stacks multiple circuit boards using ball-grid arrays to stack an SSD controller chip on top of one or more Flash memory boards to produce a component with a 1.18x1.3-inch footprint. Interface is through the BGA connections on the bottom of the cube or through a Micro SATA connector, if desired. Capacities to 256Gbytes are currently available with a transfer rate of 250 Mbytes/sec.
• mSATA or SATA mini card. This SSD employs the existing PCIe Mini Card developed for internal PC use but it re-purposes the connector by changing out the PCIe signals for SATA signals. Intel presented this idea at an earlier session at the Flash Memory Summit so it has multi-vendor support. SSDs in this form factor are currently available with capacities to 128Gbytes and with transfer rates of 100-200 Mbytes/sec.
• SSD DIMM. The SDRAM DIMM socket is ever present in most of today’s designs, embedded or otherwise, so why not use such a socket to snap in an SSD? That’s what the SSD DIMM does: it repurposes the SDRAM socket by drawing power from the existing socket and then providing an additional connector on the module’s top for a SATA cable. SSD DIMMs are currently available with capacities to 512Gbytes and with transfer rates of 260 Mbytes/sec. Using four such SSD DIMMs, you can currently fit 2Tbytes of SSD storage in the physical volume of one 2.5-inch SATA drive.

There are other SSD form factors, but this list proves that one size of SSD doesn’t fit all embedded applications.