It’s an SSD, it’s a DIMM, it’s… both? SanDisk’s new ULLtraDIMM storage device puts non-volatile flash on a DDR3 memory module. We’ll indulge the funky capitalization, because the concept is kind of cool. It’s also fairly straightforward. Instead of serving up flash storage via Serial ATA or PCI Express, the ULLtraDIMM takes a more direct path to the CPU through its memory interface.
Traditional DIMMs are based on volatile DRAM memory that doesn’t hold data when the power is cut, but ULLtraDIMMs retain their, ahem, memory when unpowered. They’re also available in much larger capacities. SanDisk is rolling out individual modules with 200GB and 400GB of 19-nm MLC flash storage.
Putting the flash right next to the CPU gives the ULLtraDIMMs especially low latency. SanDisk claims a read latency of 150 µs and a write latency of under 5 µs. The modules are said to deliver 150k random read IOps and 65k random writes. Sequential I/O is pegged at 1GB/s for reads and 760MB/s for writes, so these puppies are pretty fast all around. Impressively, SanDisk claims that performance scales linearly with additional modules—and that write latencies remain consistently low. The modules will plug into existing servers, too.
Thanks to Guardian Technology, a collection of flash management features from SanDisk-owned SMART Storage Systems, ULLtraDIMMs should have excellent endurance. They’re rated for 10 full drive writes per day for five years, which works out to over seven petabytes for the 400GB model. The flash management algorithms are also smart enough to adapt to the changing characteristics of the NAND as it wears. On top of that, the Guardian tech includes backup capacitors, end-to-end data protection, and what appears to be a RAID-like flash redundancy scheme.
SanDisk says the ULLtraDIMMs are "shipping for qualification," so enterprise types should be able to get their hands on the modules soon. IBM has already signed on to use them in its System x3850 and x3950 X6 servers, which will offer configurations with up to 12.8TB of flash.