M.2 vs mSATA case study – Crucial M500 240GB & Plextor M6e 256GB
SATA, mSATA, SATA Express, M.2, mPCIE… a bunch of terminology from which the normal customer doesn’t understand much. I must tell you that even I got confused when I found out that you can have a M.2 SSD based on a SATA controller. I knew that M.2 was the next generation high performance port allowing PCI-Express storage, so you can understand why this information was a total surprise for me and I started to research everything about this new M.2 port and its implementation in the Z97 platform.
The first thing we must clarify is the difference between connectors and protocols. M.2, SATA Express or mSATA are connectors that allows your storage device to be attached to the motherboard, while SATA and PCI-Express are protocols which is the “language” used by the devices to communicate.
SATA 3 is on the market for some time and is limited to 600MB/s, most SSD being already limited for some time by the interface. SATA 3.2 adds support for PCI-Express communication through SATA Express and M.2 interfaces, support for old SATA devices being preserved. So, in conclusion the communication protocol is being transitioned from the already obsolete SATA to the more scalable PCI-Express and we have some new connectors for this: SATA Express & M.2.
As we need it for getting all the performance out of our hardware, we must look also to the software part of this problem. AHCI (Advanced Host Controller Interface) was launched on the market more than 10 years ago, when the mechanical HDD’s were in their prime so we can say that is pretty outdated and completely not suited to high speed flash storage. While AHCI can add some performance to regular SATA 3 SSD’s, it’s totally unsuited for the high performance PCI-Express based SSD’s.
The solution comes in the form of NVMe (Non-Volatile Memory Express) – built from the ground up for SSDs and PCIe devices, NVMe has its extremely low latency compared to AHCI. This is because it doesn’t require an Uncacheable register reads to issue a command while, in comparison, AHCI needs 4 register reads per command generating an additional latency of 2.5µs. Currently there are a couple of enterprise drives that support NVMe, but consumer drives are also expected most probably with the launch of the Sandforce SF-3700 controller.
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.
ASRock Z97 Extreme6
Offcourse we couldn’t test the performance of the M.2 and mSATA storage solutions without a proper motherboard testbed. Before getting down to business we will take a look at two motherboards, representing the top models from the classic line (not Gaming or OC) of ASRock and Gigabyte.
The first in line is the ASRock Z97 Extreme6 which is the only motherboard on the market with an Ultra M.2 port. This routes 4 lanes of PCI-E 3.0 from the CPU straight to your storage device, leaving just 8 lanes for you discrete GPU or 8x / 4x if you are planning to use two GPU’s in CrossfireX (SLI doesn’t allow to be activated if you don’t have at least 8x / 8x bandwidth). Anyway don’t worry about the performance drop between 16x and 8x when running a single video card, because with modern PCI-Express 3.0 GPUs and normal resolution (1080p) you will see around 1% performance penalty.
The motherboard is shipped in a medium sized box, while the printing on it reveals some of the features that we will find on the motherboard itself. Being the top model we can find some really nice features on the motherboard: dual Gigabit LAN, 10 x SATA 3, SATA Express, regular M.2 port, Ultra M.2 port, Purity Sound 2 audio technology and a mini-PCIe if you have a WiFi card around.
The PCB of the Z97 Extreme6 is kept nice and clean, with the masive VRM and PCH heatsinks dominating the color spectrum with their blueness. The Ultra M.2 and the mini-PCIe are situated between the first and second 16x PCI-Express slots, while the normal PCI-E 2.0 2x slot is placed between the second and the third. The dual BIOS feature is also present on the board together with a switch that can toggle between them. On board Power and Reset buttons together with a Debug LED and an on-board USB 2.0 port for your USB flash disk will please for sure the overclocking crowd.
Another interesting feature is the HDD Saver, through which you can power a maximum of two HDDs or SSDs straight from the motherboard. With the A-Tuner software you can switch the storage drives on or off as you wish, but note that this feature is password protected. I find this feature very useful for privacy but also for power saving and HDD / SSD lifespan, just bear in mind that it works only in AHCI mode (not IDE and not RAID mode).
Purity Sound 2 is the name of the integrated audio card, featuring an EMI shielded Realtek ALC1150 DAC together with low noise Nichicon Fine Gold caps for filtering. The Differential Amplifier and the cap less Direct Drive technology are the same as the original Purity Sound so we see no change here.
As I said earlier, ASRock equipped the Z97 Extreme6 with 10 SATA 3 ports – 6 native from the PCH and 4 provided by 3rd party ASMedia controllers. If you have a SATA Express storage device, you are willing to give up 2 regular SATA ports and the M.2 port is not in use then you can use the available SATA Express port.
On the backpanel we can find 6 USB 3.0 ports, one PS/2 for keyboard or mouse, eSATA connectivity, two Gigabit LAN ports (Intel i218v & Realtek RTL8111GR), audio card outputs and inputs and also 3 video outputs (DVI-I, DisplayPort and HDMI). On the left of the eSATA connector we can see a little switch responsible for resetting the BIOS on-the-fly when the motherboard is mounted inside the case.
The CPU VRM on the Z97 Extreme6 is based on an Intersil ISL6379 which controls the 12 phases through ISL6611A phase doublers. The MOSFETs are D87350 made by Texas Instruments and are from the NexFET family, meaning it integrates the high-side and low-side MOSFETs in a single package. The memory VRM has two phases and is also based on TI NexFET technology, but this time they have metallic packaging for better heat dissipation.
All the heatsinks are mounted using spring loaded screws and all the solid caps are certified for at least 12.000 hours of operation. We can say that ASRock put some efforts in designing the power delivery system of this motherboard and also paid attention in choosing the capacitors.
The second motherboard presented in this article comes from Gigabyte and is the top model from their classic series: Z97X-UD5H. This model can be found in retail also in the Black Edition flavor which is tested for enhanced reliability, but you must pay 10-15$ more for this feature.
Inside the black and yellow box we can find the bundle which is very basic: user’s manual, black SATA cables, DVD with drivers and utilities, flexible SLI bridge and the – always necessary – I/O shield.
The PCB is matte black while the heatsinks are a color at the edge of gold and yellow, looking pretty good anyway. The layout is clean with three 16x PCI-Express 3.0 slots, two 1x PCI-Express 2.0, two legacy PCI slots and one M.2 port.
In the upper right corner we can find the Power, Reset and Reset CMOS buttons together with a very useful Debug LED. In the same area we have also the voltage measure points and the switches for disabling the dual BIOS feature and for changing between the two BIOSes.
The integrated audio card is based on the usual Realtek ALC1150 having the PCB around it separated for a better shielding, having added also an OPAMP on the Line Out for better headphone control and amplification. Z97X-UD5H has two Gigabit LAN controllers: Killer E2200 and Intel. I will choose the Intel anytime but hey, that’s just me :).
Gigabyte equipped the Z97X-UD5H with 8 SATA 3 ports – 6 native from the PCH and 2 provided by an additional 3rd party controller. If you have a SATA Express storage device, you are willing to give up 2 regular SATA ports and the M.2 port is not in use then you can use the available SATA Express port.
On the backpanel we can find 6 USB 3.0 ports, 2 USB 2.0 ports, one PS/2 for keyboard or mouse, two Gigabit LAN ports (Intel i217v & Killer E2200), audio card outputs and inputs and also 3 video outputs (DVI-I, D-SUB and HDMI).
The CPU VRM on the Z97X-UD5H is based on an Internatonal Rectifier IR3563B which controls the 12 phases through IR3598 drivers configured in doubler mode. The MOSFETs are SiRA12 PowerPAK’s from Vishay, each phase having one high-side and one low-side.
The memory VRM has two phases and is also based on the same MOSFET’s and chokes as the CPU VRM, the only difference being that each phase has three SiFA12 PowerPAK’s. All the heatsinks are mounted using spring loaded screws and all the solid caps come from Nippon Chemicon.
Crucial M500 M.2 240GB
The M.2 variant of the Crucial M500 is similar to its SATA 3 sibling, sharing the same Marvell 88SS9187 controller and the same 20nm Micron MLC NAND. The only difference is the M.2 format of the drive and for this reason to obtain the 240GB capacity of the drive only four NAND chips are used (512Gb each).
Although it uses the new M.2 connector, this drive is still a SATA 3 device limited at a maximum of 600MB/s because the controller used is SATA based. On the back of the M.2 SSD we can find a feature that’s standard in all Crucial M500 SSDs. I’m referring to the 20 capacitors that ensures that all information in the cache will be written completely in case of a power loss.
Plextor M6e 256GB
The Plextor M6e is also a M.2 device but one that’s much more interesting, because it’s based on a Marvell 88SS9183 PCI-E 2.0 2x controller. This translates in advertised speeds of 770MB/s read and 580MB/s write, well over the 500MB/s read and 250MB/s write that the Crucial M500 has. This is what a native PCI-E 2.0 2x controller can do, coupled off-course with high quality 19 nm Toshiba Toggle-mode NAND (64 GB dies).
The drive is delivered in a nice red box together with an M.2 to PCI-E 4x adapter for those who don’t have an M.2 connector on their motherboard. If you do have the M.2 connector then I recommend to buy the model named Plextor M6e M.2 which doesn’t come bundled with the adapter. I say this because you lose the hefty 5 year warranty that Plextor offers if you remove the drive itself form the adapter, not very nice, ah? One last thing to mention is the fact the Plextor M6e is a bootable drive so you don’t have to worry about this.
|CPU||Core i7 4790K|
|MB||ASRock Z97 Extreme6|
|RAM||2x4GB Corsair Dominator Platinum 2400 CL9|
|Cooler||Enermax Liqtech 120X + Arctic Cooling MX-4|
|Main SSD||Intel SSD 730 240GB|
|Case||Dimastech Benchtable Easy v2.5|
|Ambient temp||25 oC|
|OS||Windows 7 Ultimate x64 SP1|
Our goal today is to test both SSDs and see how they perform using the ASRock Z97 Extreme6 as our testbed. We picked this motherboard out of the two because we also want to see if we can find any difference between the normal M.2 slot and the Ultra M.2 slot. For this we will use the Plextor M6e because it is PCI-Express based and run the tests on each slot to see if switching PCI-E lanes from the PCH to the CPU helps or not.
The rest of the platform was chosen not the interfere in any way in our testing – the CPU is the latest Core i7 4790K cooled by Enermax LiqTech 120X AIO. We used 2x4GB Corsair Dominator Platinum 2400 CL9, while the PSU is the excellent Seasonic P1200.
We run the drives as secondary storage, the Intel SSD 730 240GB being the main drive with Windows 7 Ultimate 64bit SP1 installed. AHCI mode was used in all the tests and the latest version of Intel RST was installed for the Crucial M500. For the Plextor M6e we were limited to the legacy AHCI driver from Microsoft because PCI-E storage and because of Intel RST :).
Crucial M500 240GB – Results
We can see from the tests below that the Crucial M500 240GB on M.2 interface is no better than a regular SATA 3 drive of the same family. This was expected as they share the same controller / NAND / firmware. The results advertised by Crucial are real and we get the same ~500MB/s read speeds and ~250MB/s write speeds.
Plextor M6e 256GB – CPU vs PCH results
Although the sequential speeds are similar between the CPU and PCH results, we can see that the 4K results are much better when we switch to the CPU lanes. The final result in Anvil is almost 20% higher using CPU PCI-E lanes instead of PCH lanes.
The results from the Plextor M6e are in a totally different class compared to the Crucial M500. In the ATTO Disk Benchmark the results are similar between CPU and PCH lanes.
In CrystalDiskMark we see again big difference at 4K transfers between the PCH and CPU lanes. Here we see also an increase in the sequencial read speed from 728MB/s to 750MB/s.
We also see significant gains in 4K speeds in AS SSD Benchmark – we get much better results when we use CPU PCI-E lanes. In the Copy-benchmark we get better results from the PCH connection, maybe we need a good Intel RST for PCI-E drives. Let’s hope also that NVMe comes fast to the consumer market, this will be another step forward for the PCI-E storage devices.
In PCMark 8 Storage Test we get an increase in bandwidth from 318MB/s to 330MB/s which translates in a very small increase in the total score.
This article wasn’t a direct comparison between the two SSDs because they are not even in the same class or price range. I wanted to show you that even if a SSD has the latest and most greatest interface in the world doesn’t mean it’s ultra fast. Also I wanted to clarify some aspects about the M.2 standard and also test the influence of the Ultra M.2 technology from ASRock.
So, what did we learn from our study today? In the case of the Crucial M500 240GB we saw that it doesn’t matter what connector we use when the protocol stays the same, overall the drive is nice and has a good price / performance ratio. You can get the 480GB version for $265 and benefit for the extra storage and increased write speed to 400MB/s, pop into the M.2 slot and you get rid of all the ugly SATA 3 and SATA power cables.
The Plextor M6e really shinned when it was connected to the CPU PCI-E lanes and this is not something good because, at least for now, the ASRock Z97 Extreme6 is the only desktop motherboard with the Ultra M.2 slot. The M6e is in a difference performance class but also in a different price class as the 256GB version costs $220 and the 512GB you can get for $420 (both without the adapter). The price is slightly higher than most high-end SATA 3 SSDs but the performance you get is also much higher. Plextor M6e is the fastest bootable M.2 SSD that you can find in retail and that you can actually afford.
The M.2 standard is very well thought and can support further performance increase from the storage devices, while the SATA 3 cannot. Faster PCI-E 4x controllers for SSDs are already in the works and Intel will allocate PCI-E 3.0 4x lanes for M.2 in the upcoming chipsets. As expected, Intel Z97 chipset and motherboard are just a bridge between Z87 and future Skylake-ready chipsets. In the next generation we will see the real potential of the PCI-Express storage (M.2 & SATA Express), when Intel will also release Rapid Storage Technology (RST) over PCI-E.