M.2 SSD Interface Starting to Gain Traction
We have reached the point where it is possible to buy high capacity SSDs at a reasonable price. Most are still bound by the bandwidth limitation imposed by the SATA 6Gb/s interface, with the top performing Samsung's SSD 850 Pro offering sequential read and write speeds of 550 to 520MB/s.
A solution to this problem was revealed midway through 2014 with Intel's Haswell refresh. The Z97 chipset provided support for the M.2 and SATA Express interfaces, both of which were designed to take mainstream SSD performance to the next level.
The Z97 chipset, which first introduced the M.2 slot on the desktop, only supports up to eight PCIe 2.0 lanes with the rest of the PCIe lanes being used by graphics cards. All this changed with Skylake as the Z170 can support twenty PCIe 3.0 lanes through the chipset, so putting aside four of those lanes for an M.2 socket is no longer an issue.
M.2 2280 Socket
In addition to the M2 socket, the Non-Volatile Memory Express or NVMe, is a new performance controller interface set to replace the aging AHCI standard. Being more than a decade old, AHCI was designed for hard drives and is therefore optimized for high latency rotating disks rather than low latency non-volatile storage.
AHCI isn't the best interface for PCIe SSDs and thus industry leaders including Intel, Samsung, and LSI have developed NVMe with advantages such as multiple queues, higher queue depths and lower latency as NVMe allows for a direct path from the storage to the CPU.
So far SATA Express has not been widely adopted and the uptake of the M.2 socket has been slow, but things are now starting to move forward.
Samsung was the first manufacturer to show what the M.2 socket was capable of with its OEM XP941 PCIe SSD. Using four PCI Express lanes the XP941 was good for read and write speeds of 1,170 to 950MB/s.
Earlier this year the XP941 was replaced with an even faster Samsung M.2 SSD, the SM951 which boasted read and write speeds of 2,150 to 1,500MB/s and was later upgraded to support the new NVMe command set, offering even greater performance.
The latest product from Samsung is the SSD 950 Pro. Made exclusively in the M.2 2280 form factor, the SSD 950 Pro comes in 256GB or 512GB capacities.
The 512GB model boasts a sequential read speed of 2.5GB/s and a write speed of 1.5GB/s making the 950 Pro reads superior than the SM951 NVMe. It's also more affordable at $350 for the 512GB model and is widely available unlike previous OEM-only drives.
Samsung 950 Pro 512GB
The claimed sequential performance is staggering as the 512GB model boasts a read throughput of 2.5GB/s and a write speed of 1.5GB/s. The 256GB model is quite a bit slower but still blistering fast compared to any SATA SSD with a read speed of 2.2GB/s and a write speed of 900MB/s.
To achieve this kind of performance the 950 Pro series uses the PCIe 3.0 x4 interface which provides 32 Gbit/s or 3.93GB/s of bandwidth. The XP941 for example used the PCIe 2.0 x4 interface which limited it to a maximum throughput of 20Gbit/s (2GB/s) and this simply won't be enough for the 950 Pro.