R&D: FairyWREN, Sustainable Cache for Emerging Write-Read-Erase Flash Interfaces

ACM Transactions on Storage has published an article written by Sara McAllister, Yucong Wang, Computer Science, Carnegie Mellon University, Pittsburgh, USA, Benjamin Berg, Computer Science, The University of North Carolina at Chapel Hill, Chapel Hill, USA, Daniel S. Berger, Microsoft Research, Redmond, USA, Nathan Beckmann, Computer Science, Carnegie Mellon University, Pittsburgh, USA, George Amvrosiadis, Carnegie Mellon University College of Engineering, Pittsburgh, USA, and Gregory R. Ganger, Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, USA.

Abstract: “Datacenters need to reduce embodied carbon emissions, particularly for flash, which accounts for 40% of embodied carbon in servers. However, decreasing flash’s embodied emissions is challenging due to flash’s limited write endurance, which more than halves with each generation of denser flash. Reducing embodied emissions requires extending flash lifetime, stressing its limited write endurance even further. The legacy Logical Block-Addressable Device (LBAD) interface exacerbates the problem by forcing devices to perform garbage collection, leading to even more writes.“

“Flash-based caches in particular write frequently, limiting the lifetimes and densities of the devices they use. These flash caches illustrate the need to break away from LBAD and switch to the new Write-Read-Erase iNterfaces (WREN) now coming to market. WREN affords applications control over data placement and garbage collection. We present FairyWren, a flash cache designed for WREN. FairyWren reduces writes by co-designing caching policies and flash garbage collection. FairyWren provides a 12.5 × write reduction over state-of-the-art LBAD caches. This decrease in writes allows flash devices to last longer, decreasing flash cost by 35% and flash carbon emissions by 33%.“