So I am a few thousand miles above beautiful California and the 2013 LSI Accelerating Innovations Summit. I can’t help but reflect on the confusion that still exists concerning the standardization of M.2 SSDs, regardless of how many times we try to explain this in our reports (1, 2, 3). If you are confused and not an industry professional, don’t be embarrassed. Many storage insiders are just as confused and also realizing that there really is no standardization with M.2 SSDs.
To compound things, there were no PCIe X4 M.2 SSDs on display at the AIS, and with good reason, according to the SandForce Marketing Team. While everyone at the show might have expected LSI to build and show a PCIe x4 M.2, it looks like they are initially focused on the larger majority of PCIe x2 M.2 systems out now. The standard PCIe x4 HHHL board they did show certainly proved the SF3700 can hit the PCIe bus 1800 MB/s limit.
WHERE DID THE NAME M.2 COME FROM?
Some time ago, the Gods responsible for SSD standardization realized that there were just too many small form factor SSD types. In their wisdom, they decided to take a crack at standardizing future PC systems by incorporating a standard connection, called a M.2 connector (or host). Initially, they didn’t want to give an SSD the name of a connector, so the name NGFF was born, meaning ‘Next Generation Form Factor’. A bit amusing perhaps is the fact that, even today, NGFF remains to be a more recognizable name than M.2 itself , and also provides much more specific results when doing a Google search.
As much as so many of us would love the M.2 host to be the ‘holy grail’ of SSD standardization, it’s not. It is a connector, and a female one at that. It is not restricted to SSD use alone, and can also be utilized for Wi-Fi, WWAN, Bluetooth, GPS, NFC, as well as several interfaces to include PCIe and SATA. A key point here is that PCIe and SATA are different interfaces and one cannot be reached via the other, meaning, these SSDs cannot be simply switched off in M.2 capable systems. As we are learning, the only REAL standardization is the connector itself. The male connector on the SSD is not standardized and can be either of the two shown here:
UNDERSTANDING M.2 SSD KEYING
This picture depicts two SSDs, the Samsung XP941 native PCIe SSD (reviewed), which operates at a theoretical high of 1.4GB/s, and Toshiba’s first M.2 SSD release (also reviewed), which is a SATA 3 SSD and will hit typical 6Gbps highs of 575MB/s. You will notice that the connector of the Samsung SSD has one notch separating two sets of contacts; this is termed the ‘M’ key. Similarly, the Toshiba has two notches and these are known as the ‘M’ and ‘B’ keys, just as you see in this PCIe Gen 2 X2/SATA 6 Gb/s 80mm M.2 SSD featuring the new SF3700 flash controller.
Only the single ‘M’ keyed SSD can reach those lightning fast speeds that we have seen in the Samsung XP941, and will be evident in SSDs containing the LSI SandForce SF3700 flash controller. This is because only the single ‘M’ keyed connector connects by PCIe X4. A single ‘M’ Keyed connector can also be used for SATA, but that would make as much sense as throwing the body of a Ferrari on a Ford Focus.
To carry this a bit further for those relatively new to data travel, PCIe Ver. 2.0 is capable of a maximum transmission rate of approximately 500MB/s per lane. Four lanes (X4) enables speeds up to 2GB/s (4x500MB/s) as we might see in the Samsung XP941 and LSI SandForce SSDs. PCIe 2.0 X2 will allow speeds up to 1GB/s (2x500MB/s) and we will soon see this first hand with the Plextor M.2 PCIe X2 SSD, named the M6e.
This picture illustrates the new LSI 3700 flash controller on a PCIe 2.0 X4 M.2 SSD, for the first time, and we felt it important that the reader see both together. This combination is the only that will enable lightning fast 1.8GB/s speeds from an M.2, and subsequently, the smallest and fastest SSD in the world. A click on this picture will display it in a higher resolution and, as well, this video might explain why the SF3700 just may be groundbreaking entry into the SSD arena: