SSDs have continued to mature as manufacturers search for refined methods to exploit the high performance and low latency of flash. What initially began as standard 2.5" drives with SAS/SATA connections, morphed into PCIe-connected SSDs and M.2 designs that communicate via the PCIe bus to achieve lower latency. New standards, such as NVMe, have even come to fruition (covered in our Defining NVMe article). Each step on the path to creating the perfect storage device has resulted in tangible benefits, but the ULLtraDIMM has taken what could be the final step, short of fusing a storage medium onto the CPU itself. The SanDisk ULLtraDIMM DDR3 SSD brings latency as low as five microseconds by sidestepping the traditional storage stack, and communicating via the DDR3 bus.
The first time I heard of ULLtraDIMM was during a press briefing with John Scaramuzzo, then the CEO of SMART Technologies, and now Senior Vice President and GM of SanDisk's Enterprise Storage Solutions team. SMART was a scrappy upstart spinning their way to becoming a behemoth of the enterprise SSD world, and John described several of the challenges of bringing such a revolutionary technology to market. Not only did they need to develop the product, but they also had to create an ecosystem of test, validation, and field support tools. They also needed to forge partnerships with OEM's to bring the product to market.
The initial key partnership was with Diablo Technologies, a Canadian company with ten years of experience in the memory subsystem space. Diablo developed the Memory Channel Storage (MCS) architecture (covered in more detail on the following pages), which delivers end-to-end parallelism by leveraging the memory subsystem. MCS's current incarnation works with NAND flash, but the forward-thinking architecture can also support future non-volatile memory technologies. Diablo provides the reference architecture, DDR3-to-SSD ASIC and firmware, kernel and application-level software development, OEM system integration, and ISV partnerships.
Another big step came when SanDisk acquired SMART in July of 2013. The move to SanDisk enabled direct access to NAND manufacturing and engineering, along with a wide range of OEM partnerships in the global market. SanDisk provides the SSD ASIC and FTL firmware development and testing, the Guardian Technology Platform, supply chain, manufacturing, and system validation.
Eventually, ULLtraDIMMs (Ultra Low Latency DIMM) will be plug-and-play with in-box drivers, but initial revisions will require UEFI BIOS modifications. OEM integration is important to provide compatible platforms. IBM (now Lenovo) was the first OEM to deploy ULLtraDIMMs, up to 12.8 TB per system, rebranded as eXFlash in their System x3850 and x3950 X6 servers. Supermicro followed suit, and is integrating ULLtraDIMMs into seven different models in their Green SuperServer and SuperStorage platforms. Huawei recently announced RH8100 V3 servers will feature an ULLtraDIMM option, and Diablo has mentioned that other OEM partnerships are in the works.
The hardware consists of a JEDEC-compliant ULLtraDIMM that presents itself as a block storage device with 200 or 400GB of capacity. The ULLtraDIMM utilizes two Marvell 88SS9187 controllers running the Guardian Technology Platform to increase endurance and reliability. This tandem delivers random read/write performance of 140,000/40,000 IOPS, and sequential read/write speeds up to 880/600 MB/s. Ten DWPD (Drive Writes Per Day) of endurance, and a five-year warranty (or TBW) are provided by SanDisk 19nm eMLC NAND. The ULLtraDIMM also sports a 2.5 million hour MTBF, and host power-loss protection. The most important attribute is latency as low as five microseconds. This even undercuts new NVMe PCIe SSDs, which hover around 20 microseconds.
Robust ten DWPD endurance enables the ULLtraDIMM to satisfy the requirements of write-intensive and mixed-workload applications. It is well suited for HPC, HFT, transactional workloads, big data, analytics, VDI, and cloud computing architectures. ULLtraDIMMs distributed architecture exploits parallelism for performance advantages, and scales to meet the capacity and performance requirements of applications. The ideal configuration for an ULLtraDIMM deployment is four to eight DIMMs at a minimum, but the platform scales up to 32 DIMMS and 12.8 TB of storage. It is important to note that our evaluation only utilizes two ULLtraDIMMs for testing.
With the players in position, SanDisk and Diablo are poised to radically alter server-side flash utilization. ULLtraDIMM will enable new designs for blade and microservers by eliminating HAD/RAID controllers, cabling, and complexity. SanDisk has displayed incredibly small servers with impressive storage density at several trade shows. Let's take a closer look at the technical aspects of the ULLtraDIMM.
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