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When Computer Weekly last surveyed PCIe SSD products in November 2013, the theme was the consolidation of the industry through multiple acquisitions.
This time around similar trends are still occurring with the demise of products from Violin Memory, the SanDisk's acquisition of Fusion-io and Seagate's move into PCIe SSD through its acquisition of LSI's Nytro product line.
From a technical perspective, performance and capacities haven't increased significantly in the most recently released products. There remain roughly equivalent levels of performance, bandwidth and latency compared to products shipped previously. Only a handful of suppliers have moved to support PCIe 3.0, with many still shipping the PCIe 2.0 connectivity reported 18 months ago.
One major change has been the emergence of support for new form factors and protocols, including NVM Express (NVMe).
NVMe reduces the overhead associated with accessing PCIe SSD devices that currently use SAS/SATA protocols (AHCI) and allows them to take advantage of the parallelism of the latest PCIe 3.0 specification. Devices use either the existing PCIe AIC (add-in card) HBA-style adaptor or the SFF-8639 connector when devices are delivered using the 2.5" drive form factor.
The PCIe SSD suppliers surveyed in April 2015
M.2 entrants could threaten NVDIMM
Suppliers have started to release products that use the M.2 (formerly NGFF or Next Generation Form Factor) connector and form factor for their products. Currently these are targeted at consumer devices and, while they aren't mainstream in the server space, they could represent a challenge to technology such as NVDIMM if motherboard suppliers choose to provide the ability to connect many devices in a single chassis.
Almost all PCIe SSD suppliers continue to use MLC flash in their products. We should expect TLC to be on the horizon, as this technology (which delivers lower-cost, higher-capacity drives at the expense of endurance) matures - but it is likely to be some time before it arrives in enterprise devices, especially those physically tied to the server (requiring a reboot/power down to remove).
Also expect to see 3D-NAND arrive. This will increase densities and favour the smaller form factors, but may have issues achieving density at PCIe power specifications.
Regarding the product roundup, it is worth remembering that, with all PCIe SSDs, the choice of the most appropriate device depends on requirements -- either high bandwidth or low latency -- at the most appropriate cost.
Once seen as a leader of the PCIe SSD industry, Fusion-io lost its direction somewhat and was eventually bought by SanDisk in 2014.
A shadow of its former self, Fusion-io now offers two products under the Atomic Series, the PX600 and PX300. The PX600 targets high endurance workloads, whereas the PX300 offers similar capabilities at higher capacity, but without the endurance capabilities.
Both platforms provide up to 2.7GBps (read) and 1.6GBps (write) bandwidth (with the ability to reach 2.1GBps write using high power mode), 285,000/385,000 read/write IOPS and 92µs/15µs read/write latency. It's interesting to note that the simplification of previous products into the Atomic series also increased read latency by around 35%.
Fusion-io's legacy ioDrive products are still available and don't appear to have been upgraded recently. Endurance figures are proportional to capacity, with the highest capacity devices quoted at 64PBW (64 petabyte writes).
Intel has recently announced the Intel SSD 750 Series (pictured above) that uses the PCIe 3.0 (x4) interface.
The 750 is available in either 400GB or 1.2TB capacities, and as either an AIC (add-in card) or the 2.5" form factor. Although this product and the 535 Series (M.2 form factor) target the consumer market, these devices are still remarkably fast (20µs read/write typical with the 750 series) and could point the way to future enterprise-class developments. The only downside of these devices is the relatively low endurance (219 TBW -- terabytes written) for a typical 750 Series drive.
On the datacentre side, Intel offers the SSD DC P3700 Series, using either the AIC or 2.5" drive form factor with PCIe 3.0 x4 connectivity. The P3700 offers capacity up to 2TB (using 20nm MLC NAND flash) 2.8GBps read and 2.0GBps write bandwidth, up to 460,000/175,000 read/write IOPS at a latency of 20µs. Compared to the consumer products, endurance is much higher at a typical 65.7 PBW (petabytes written).
In May 2014, Seagate Technologies acquired the flash business of LSI from Avago Technologies. Avago had only acquired LSI six months earlier in December 2013. The deal allowed Seagate a relatively cheap entry ($450m) into the PCIe SSD market and, in September 2014, the company announced two new products: the Nytro XP6209 and the Nytro 6302. The XP6209 uses MLC NAND flash and is based on the PCIe 2.0 interface, whereas the XP6302 uses eMLC and PCIe 3.0 (x8).
The Seagate Nytro XP6209 provides up to 1.86TB of usable capacity with bandwidth figures of 2.0GBps and 1.27GBps for read and write I/O respectively. Average latency is quoted at less than 50µs (although this isn't broken down by the supplier into read/write capabilities) with up to 185,000 read and 120,000 write IOPS respectively.
The Nytro XP6302 offers up to 1.75TB of usable capacity with a performance rating of 300,000 read IOPS and 120,000 write IOPS. Latency is quoted at less than 200 microseconds, which is surprisingly slower than the XP6209 counterpart. The XP6302 does, however, offer decent bandwidth at 3.9GBps (read) and 2.5GBps (write) respectively.
Read more about flash storage
Micron continues to offer the P320h and P420m PCIe SSDs, available in either AIC (add-in card) or 2.5" form factors. Both support the PCIe 2.0 specification.
The P420m scales to 1.4TB in capacity with a bandwidth rating of 3.3GBps (read) and 630MBps (write) for the AIC model. The 2.5" form factor is rated slightly lower at 1.7GBps and 500MBps respectively.
A similar difference is seen with IOPS performance. The AIC is rated at 750,000 (read) and 95,000 (write) IOPS whereas the 2.5" model is 400,000/51,000. Both models offer similar latency figures (100µs read, 15µs write). The P320h is based on SLC NAND at 34nm process, delivering up to 415,000 (read) and 145,000 (write) IOPS.
Samsung Electronics offers two PCIe-based SSDs, using either the 2.5" (XS1715) or AIC (SM1715) form factors. The XS1715 is available in capacities up to 1.6TB, with an endurance rating of 7 device-writes per day (DWPD) -- equivalent to about 20 PBW. The drive delivers around 750,000 read IOPS and 115,000 write IOPS with a bandwidth capability of 3GBps (read) and 1.4GBps (write).
By comparison, the SM1715 offers slightly better write performance (130,000 IOPS) and a higher endurance at 10 DWPD. Both drives support the NVMe specification.
Samsung has also recently announced the SM951, a consumer specification PCIe SSD based on the M.2 form factor and using PCIe 3.0 x4. As previously noted, these devices may well see their way into enterprise class products in the future.
HGST has begun to release PCIe SSD products under its Ultrastar brand name, following on from the acquisitions of STEC and Virident a few years ago. The Ultrastar SN100 scales up to 3.2TB in capacity and supports PCIe 3.0 and NVMe specifications in either AIC or 2.5" drive form factors.
The SN100 is capable of 3GBps (read) and 1.6GBps (write) bandwidth and up to 743,000 IOPS (read) and 160,000 IOPS (write) and latencies of less than 20µs (only write latency figures specified). Endurance is rated at a relatively low 3 DWPD.
Memblaze is a relative newcomer to the market, founded in 2010 and based in China. The company offers two products, PBlaze3L (up to 2.4TB) and PBlaze3H (up to 4.8TB), both based on PCIe 2.0 (x8) and the AIC form factor. The devices claim high performance with the PBlaze3H model capable of 750,000 IOPS (read) and 240,000 IOPS (write) with 3.2GB/s (read) and 2.2GB/s (write) bandwidth, all at 80µs read and 14µs write latency. However endurance is relatively low at only 3DWPD.