Fusion-io's chief operating officer Lance Smith is going around lancing the boil that is the flash DIMM – flash memory interfaced to a server's memory bus instead of its slower PCIe interface – but he's facing a challenge from Diablo Technologies.
Flash DIMM technology is provided by Diablo Technology to SanDisk, which has used it in its ULLtraDIMM product and licensed it to IBM and Supermicro ,with more server vendors expected to come on board.
Yet Diablo Technologies' CEO, Ricardo Badalone, thinks that his memory channel technology will take over much of the PCIe flash market, meaning he sees his tanks parked on Fusion-io's lawn.
What does Fusion-io think of this? Mr Smith agrees that flash DIMMs have a specific advantage over Fusion-io's PCIe flash (ioMemory) when data has to be written fast into a buffer but not otherwise, and quotes numbers to prove it:
- Read latency - Fusion-io - 68 microsecs vs flash DIMM's 100 microsecs
- Write latency - Fusion-io - 15 microsecs vs flashDIMM's <5 microsecs
He says Fusion-io's read and write performance is pretty symmetrical while flash DIMM's is not. Flash DIMMs are good for high-speed messaging needs in trading applications but this is niche and not generic.
Smith also points out that comparing a number of flash DIMMS at a certain capacity level to a single PCIe flash card is not an apple-for-apples comparison: "Put 8 ULLtraDIMMS in one system for parallel access and put 8 Fusion-io cards in parallel too and you'll get an order of magnitude improvement in performance."
Fusion-io cards have a greater power budget than ULLtraDIMMs meaning you can get more flash capacity with them.
Also putting flash DIMMs into a server takes away DRAM DIMM slots. In a 4-slot server, putting in two ULLtraDIMMs cuts your DRAM capacity in half. Memory runs faster than flash; flash should be used as an adjunct to memory and not a replacement. That's what happens with Fusion-io's support of SQL Server 2014's Buffer Pool Extension (BPE) functionality. The flash acts as a L2 cache to main memory (L1) which is effectively a cache for the CPUs and their cores.
If flash DIMM limitations could be remedied then, maybe, Fusion-io could use the technology, but for now, Smith says, general server flash access latency is not the bottleneck; it's the interaction between DRAM and flash, with software, like SQL's BPE, needed to use server-resident flash to its best advantage.
Diablo's flash DIMM tanks may be trying to mess up Fusion-io's lawn but they won't make much of an impression. ®