M.2 vs mSATA case study – Crucial M500 240GB & Plextor M6e 256GB
The M.2 interface, formerly knows as NGFF (Next Generation Form Factor), was introduced following the need of a compact connector that can work with SATA, PCI-Express and USB based devices. This will replace the already aging mSATA and mPCIE connectors which are not very flexible and also bandwidth limited.
The M.2 connector was introduced by ASUS on their Z87 ROG series of motherboards but only with 1x PCI-Express 2.0 connection (only 500MB/s maximum possible transfer rate). ASRock followed the trend and put the M.2 connector with 2x PCI-Express 2.0 lanes attached in its Fatal1ty 990FX Killer motherboard. This was just some early pioneering as the M.2 devices weren’t really available at that time.
The M.2 connector became a standard on virtually all the motherboards when Intel launched its Z97 Express chipset, officially announcing SATA Express and M.2 support. Intel specifies 2x PCI-Express 2.0 lanes for this, for a total bandwidth of 1000MB/s, a nice boost from the 600MB/s of the old SATA 3.
Basically, the M.2 standard is a small form factor implementation of the SATA Express interface (SATA 3 and PCI-Express connection) with the addition of an USB 3.0 connection. Due to the shared nature of PCI-Express and SATA lanes on the Z97 motherboards, you can only use one of these connection at a time (if you use SATA Express then the M.2 connection is unavailable and the other way around). The PCI-SIG specification of the M.2 standard provides 4x PCI Express 3.0 lanes and one SATA 3 port through the same connector, allowing use of both PCI Express and SATA storage devices.
Although Intel limited the bandwidth of the M.2 slot implementation in its Z97 Express motherboards to 1000MB/s (2x PCI-Express 2.0), ASRock decided to take one step forward on its Z97 Extreme6 motherboard and connect the M.2 slot to 4x PCI-Express 3.0 taken straight from the CPU. This means that we will have better latency due to the direct CPU connection but also much higher bandwidth (3940MB/s) due to double lanes and PCI-Express 3.0 instead of 2.0.
While all this sound very good, the main problem here is that we cannot find on the market today any PCI-E 3.0 compatible M.2 storage devices. The best M.2 SSD available in retail is the Plextor M6e based on a PCI-E 2.0 2x Marvell controller, which we will test today. For comparison we threw in also the mainstream SATA based Crucial M500, just to see what we can expect from the new generation of devices.
While the Plextor M6e is the best M.2 SSD that can be found in the stores, in the wild we can find also the Samsung XP841 which is an OEM drive destined for integration in high performance ultrabooks. This little monster is based on a PCI-E 2.0 4x high-performance controller similar to the one used in the SATA based Samsung 840 EVO.
Some retailers in the US saw the opportunity and started to sell these OEM drives so this is the reason we cannot consider the XP841 as a retail drive, because it is not available everywhere and the stock is limited. Also, besides the benchmark afficionados this SSD is not very useful because it’s not bootable in most Windows environments and also TRIM implementation is not fully functional. In comparison, the Plextor M6e is a retail product, bootable in every OS you can think of and with a highly efficient Garbage Collection.