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In recent months Computer Weekly has surveyed the key players in all-flash arrays (startups and big six storage suppliers), hybrid flash arrays and flash caching software. Here we take a look at the other key options in the flash storage market -- PCIe flash or server-side flash.
As storage has diversified in the datacentre, the PCIe SSD marketplace has matured and the range of available products has increased.
PCIe flash goes into the PCIe slot in the server; it’s a connectivity method that bypasses the need for a SAS or Sata controller in the server, so latency is much lower than the equivalent SAS/Sata-connected solid-state disk. Lower latency allows increases in throughput measured in IOPS and megabytes per second (MBps) throughput rates.
In the past 12 months the market has consolidated, with the acquisition of STEC and Virident by Western Digital’s HGST arm. This changes things for the likes of Seagate, which was reselling Virident hardware as its X8 PCIe Accelerator.
It is clear that Western Digital wants to expand out of its traditional hard drive base, as growth in that market contracts and solid-state becomes more widely adopted.
And over the past couple of years, Fusion-io – seen as a pioneer in PCIe flash -- has seen its leadership role eroded. As we will see, these days there is very little to differentiate hardware from Fusion-io and other market players such as LSI, OCZ, Intel and Violin.
Meanwhile, earlier this year all-flash array maker Violin Memory joined the PCIe SSD fray with its Velocity card range. It seeks to differentiate itself from the competition by taking IP from its VIMM technology, including vRAID, to provide high levels of device reliability.
As new companies enter the market, IBM appears to have dropped PCIe hardware from its Texas Memory Systems acquisition and is reselling Fusion-io in its place, rebranded as the High IOPS SSD PCIe Adapter range.
From a technical perspective, the major vendors continue to sell products based around the PCIe 2.0 specification, using four-lane or eight-lane implementations, the latter providing higher performance with the ability to deliver more parallel I/O.
Fusion-io uses 16-lane on its Octal product, its highest capacity models. We are starting to see some support for PCIe 3.0 and some suppliers support the new 2.5in form factor in their product ranges.
As always, PCIe SSD devices depend on driver software to get the best performance and as yet there are few standards in place, so the quality of driver software can be as important as the hardware. It should be noted that all metrics quoted are vendor-supplied.
Fusion-io has four PCIe flash storage product lines, including ioCache, ioDrive II, ioDrive Duo, ioDrive Octal and ioFX. All are targeted at the server market, except ioFX, which is aimed at workstation applications.
The ioDrive II products range from 365GB to 3TB in capacity, with no write latency advantage for single-level cell (SLC) over multi-level cell (MLC) products. However, these do see a 45% performance improvement for read latency. The Duo models have similar latency figures, but see double the throughput as they use eight-lane PCIe connectivity.
For large capacity applications, ioDrive Octal cards offer up to 10.24TB of MLC flash, at up to 6.7GBps and 3.9GBps read and write throughput, but this is at the cost of write latency. These devices are not for the faint hearted, consuming up to 150W of power each.
Intel continues to offer its 910 Series devices in capacities of 400GB and 800GB, based on 25nm process MLC flash. The 910 uses the PCIe 2.0 x8 interface and has latency times of 65µs for read and write I/O.
Performance scales with capacity (as the 800GB uses four Nand modules compared with two in the 400GB device) to a maximum of 2GBps and 1.5GBps for read and write throughput respectively. We can expect to see the next increment of Intel’s PCIe SSD technology some time in 2014.
The LSI Nytro product range includes Warpdrive and MegaRAID.
Warpdrive, which acts as a standard server acceleration product comes in SLC versions, branded WLP4, and eMLC versions branded BLP4, with maximum capacities of 400GB and 1600GB respectively.
Unfortunately, LSI does not provide detailed performance metrics for these devices other than to state latency is less than 50µs, so it is difficult to rate them against the rest of the market.
The MegaRAID devices are designed to accelerate direct-attached storage (DAS) in a server, connecting to SAS devices and using the latest PCIe 3.0 specification. Performance for these devices will vary depending on the workload profile, but they do include Raid support (0, 1, 5 and 6) with up to 128 external SAS or Sata devices.
Both models peak at around 3GBps throughput with the P320h offering the lowest supplier-quoted write latency in the products reviewed, at 9µs.
As well as its consumer products, OCZ produces a range of enterprise devices under the Z-Drive brand. The Z-Drive R4 CM84 and RM84 devices use PCIe 2.0 x8 in a low-profile form factor and capacities up to 1.2TB using MLC flash.
OCZ provides few performance metrics other than a symmetric read and write bandwidth of 2GBps and write IOPS of up to 250,000 with 4KB blocks.
The CM88 and RM88 devices use larger full height ¾ length cards and scale up to 3.2TB in capacity, with 2.8GBps throughput and 410,000 IOPS at 4KB.
The “C’ and “R” models are differentiated by additional hardware logic which provides greater data integrity in the event of power loss on the “R” models.
STEC and Virident
STEC offers a range of products under the s1120 PCIe Accelerator brand. These devices scale up to 200GB with SLC and 1.6TB with MLC flash, delivering throughput of 1.4GBps and 1.1GBps for read and write I/O respectively.
Virident offers three classes of its FlashMax II product, branded Capacity, Performance and Standard.
The Capacity model provides 4.8TB of MLC flash at up to 2.6GBps read throughput (with 64KB blocks), but only 900MBps for write I/O.
Both the Standard and Performance models appear to be based on the same technology, with Performance offering twice the capacity and twice the throughput of the Standard models, but with similar latency figures. This shows the increase is being achieved by using more controllers and data paths.
As previously mentioned, STEC and Virident are now owned by HGST so some product harmonisation is likely.
Violin Memory entered the market early in 2013 with its Velocity range of PCIe SSD devices that use IP developed for their existing storage array products. This includes vRAID technology that can provide on-card redundancy and RAID protection across multiple cards with driver software.
The three Violin PCIe flash models are L13, H27 and H55, scaling to a maximum of 3.2TB. Latency figures are broadly comparable to the perceived market leader Fusion-io at 70µs and 15µs for read and write respectively.
However, the Velocity devices fail to deliver on write throughput compared with Fusion-io, with a maximum of 405MBps on the H55 model. It should be noted, however, that Violin is the only supplier to quote peak and sustained performance figures (the sustained ones are used here) and so on peak numbers they outperform Fusion-io quite comfortably.
There are also products available from EMC (XtremSF), which rebrands OEM products from the existing listed manufacturers.