No, M.2 (pronounced M-dot-two) is not a government spy organization or secret project. It’s a small-form-factor (SFF) multi-purpose connector designed to replace the small mSATA and mini-PCIe slots commonly used in laptops. As such, M.2 isn’t designed strictly for storage, (it supports USB, SATA, and PCIe), but storage is a large part of what’s driving its adoption—even on the desktop.
Say what? The thing is, M.2’s PCIe connectivity has coincided nicely with the migration of SSD drives to PCIe, to sidestep the 600MBps limitation of the SATA bus. The marriage of PCIe and the SSD has resulted in uber-fast storage for your PC.
PCIe SSDs simply blow their SATA brethren out of the water in terms of sequential throughput, and in the case of NVMe, queued small writes.
When I say uber-fast, I’m talking nearly four times the speed of SATA. Yup: 2GBps. It’s hard to describe how smoothly your system runs with a x4 PCIe M.2 SSD on board. But I’m going to try, and also let you know which of the currently limited, but excellent selection of M.2 SSDs you should buy. Note that there are also SATA M.2 SSDs, but they’re subject to the 600MBps limit. Boring, but handy if that’s all your laptop supports.
Don’t have an M.2 slot on your system? If you’re talking about a desktop, you’re in luck. Simply add a $25 PCIe M.2 expansion card, such as the Addonics AD2M2S-PX4 PCIe we used for some of our testing.
Head to head
We took six M.2 SSD drives for a spin. The state of the art was represented by these drives:
The $240, 256GB Samsung SM951 PCIe (AHCI)
The $240, 256GB Samsung SM951 PCIe (NVMe)
The $499, 480GB Kingston HyperX Predator PCIe (AHCI)
We also ran a last-generation $200, 256GB Samsung XP941 PCIe (AHCI) through its paces.
Also included are two SATA M.2 drives:
An older $300, 320GB Intel 530
A newer $99, 256GB Samsung EVO SATA drive
To be perfectly honest, we included SATA drives only to show you the enormous performance gains offered by PCIe. Sneaky, eh?
Lastly, there was the aging $220 Plextor M6e, the first M.2 PCIe (AHCI) drive we ever tested. It’s included to show just how far things have come in a little over a year.
You may have noticed the parentheses indicating whether the PCIe drives were AHCI (Advanced Host Controller Interface) or NVMe (Non-Volatile Memory express). AHCI is basically the SATA protocol implemented over PCIe (or any bus really), while NVMe is a new communications protocol designed from the ground up for non-volatile storage. AHCI over PCIe removes the 600MBps bandwidth limit, but NVMe offers some advantages for multi-threaded operations, as you’ll see in the 4K queued test results seen below.
The only issue with NVMe is that your system must support booting from it. All the motherboards I’ve seen that offer a PCIe-enabled M.2 slot allow booting from NVMe, but if you’re adding M.2 to your desktop via a PCIe expansion card, you may need to go AHCI. Any motherboard of relatively recent vintage should support booting from AHCI.
Performance
All testing was done on an Asus X99 Deluxe/U3.1 motherboard with 32GB of DDR4 and an Intel Core i7-5820K. We used the motherboard’s integrated PCIe-only M.2 slot for the AHCI/NVMe SSDs, while SATA drives were tested using the aforementioned Addonics AD2M2S-PX4 PCIe expansion card. Note that the AD2M2S-PX4 doesn’t have a dedicated SATA HBA (host bus adapter). It simply uses SATA cables from the motherboard that plug into the card.
PCIe M.2 drives rock when it comes to raw sequential throughput.
As you can see from the charts, the results were split dramatically by technology. The PCIe drives won by huge margins in flat-out sequential read speed, something you’ll notice when you copy large files. NVMe proved faster than AHCI when it’s fed small files from multiple queues (the AD SSD 4K/64 threads test). Whether this scenario occurs depends upon your operating system and NVMe driver.
When threaded, NVMe can really strut its stuff with small files. It’s the reason NVMe showed up in servers first.
Keep in mind that M.2 PCIe, and PCIe drives in general, are relatively new technologies. The SM951 AHCI, only a single generation removed from the XP941 AHCI, is dramatically faster. Both are x4 PCIe, but the XP941 is PCIe Gen 2 (500MBps per lane), while the SM951 is PCIe Gen 3 (1GBps) PCIe. But even the x4 PCIe 2.0 provides 2GBps of bandwidth, so that can hardly explain the entire disparity.
The difference in small file performance between SATA and PCIe isn’t as dramatic, but still shows the advantages.
Having previously experienced only the Plextor, Kingston and XP941 AHCI drives, we were surprised and pleased to see that the SM951 AHCI was competitive with its NVMe sibling. Also note that in our real-life 20GB tests, the Kingston proved almost as fast as either Samsung drive.
All these drives are faster than SATA-bound SSDs, writing a single large file, but the Plextor M6e is actually slower than some when it came to writing small files and folders.
We’ve seen well over 2GBps from Intel’s 750 series NVMe PCIe card drive, which plugs into a an open PCIe slot like a video card (an alternative to M.2 that desktop users should consider), so the SM951 NVMe may not be showing the full potential of NVMe. Intel told us it didn’t produce an M.2 version of the 750 because at top speed, the power draw exceeded what’s available from M.2 slots. Basically, not all the ducks are in a row yet to fairly evaluate AHCI versus NVMe. It is safe, however, to say that PCIe SSDs obliterate their SATA cousins in terms of raw sequential throughput. They also occupy a slot in your motherboard.
Here are the details on the drives involved in the testing.
0 comments:
Post a Comment