The Wikibon consultancy has taken an idea put forward by Fusion-io founder David Flynn and formulated a flash-as-memory-extension concept (FaME).
The concept involves getting rid of external IO for IO-bound applications by running them and their data entirely in logical memory.
Instead of having data stored on disk, which is the second slowest of all on-line media to access – the slowest being tape – it is held on flash. Yet that flash is not in SSD format attached by SATA or SAS connections; instead it is mounted on PCIe cards.
Then again, instead of being accessed as a very-fast-but-still-external device, it is treated as a logical extension of memory so that a data access is simply a referral to another part of the application's address space and does not need the host operating system to undertake an IO at all.
That means very much faster application run-times. A main memory reference can take 100ns whereas fetching data from an SSD can take 150,000ns (0.15ms) or longer. For comparison a disk seek can take 10,000,000ns (10ms).
Wikibon consultancy's FaME concept. The yellow blocks are DRAM, the blue block processors and the stippled yellow block the PCIe flash and very low latency, high bandwidth switching
By treating flash as memory, data access is faster than from SSD, although still slower than from DRAM. Flash is less expensive than DRAM and will become cheaper with 3D NAND, meaning larger amounts can be used so that application working sets can fit into logical memory and a FaME server could host ten or even a hundred times more virtual machines.
Wikibon's David Floyer has produced a research study: “Flash as Memory Extension is the Dominant Architecture for Enterprise Performance Computing.
EMC's coming DSSD system may well embody these concepts. Check out Floyer's report; it could be a ground-breaking one. ®