IBM has revealed efforts to create a Phase Change Memory NAND card that lowers the latency of enterprise PCIe flash upto 12 times. The PCM/NAND card completes data writes 275 times faster than consumer SSDs. Before IBM’s discovery, PCM could not be taken to the product stage to its relatively high write latency. IBM’s Ioannis Koltsidas designed the Prototype Storage Subsystem (PSS) which combined NAND and PCM. According to Koltsidas the PSS’s configuration minimises write latency while maintaining an optimal read performance.
“The design of PSS targets storage workloads that are dominated by small (eg, 4 KB) random I/O operations and aims to achieve low, predictable latency with reads and writes.” – Ioannis Koltsidas
The PSS delivers 65k read IOPS at 35 microseconds and 15k write IOPS at 61 microseconds. This may well be improved if newer PCM chips are utilized – IBM’s demo used 18 month old PCM wafers. Koltsidas feels that PCM may still flourish. Use cases suggested for PCM include as a caching device, metadata store and backend for low-latency key-value store.
