FMS 2016: Facebook Talks WORM QLC NAND Flash, Benchmarks XPoint
Subject: Storage | August 9, 2016 - 05:59 PM | Allyn Malventano
Tagged: XPoint, Worm, storage, ssd, RocksDB, Optane, nand, flash, facebook
At their FMS 2016 Keynote, Facebook gave us some details on the various storage technologies that fuel their massive operation:
In the four corners above, they covered the full spectrum of storing bits. From NVMe to Lightning (huge racks of flash (JBOF)), to AVA (quad M.2 22110 NVMe SSDs), to the new kid on the block, WORM storage. WORM stands for Write Once Read Many, and as you might imagine, Facebook has lots of archival data that they would like to be able to read quickly, so this sort of storage fits the bill nicely. How do you pull off massive capacity in flash devices? QLC. Forget MLC or TLC, QLC stores four bits per cell, meaning there are 16 individual voltage states for each cell. This requires extremely precise writing techniques and reads must appropriately compensate for cell drift over time, and while this was a near impossibility with planar NAND, 3D NAND has more volume to store those electrons. This means one can trade the endurance gains of 3D NAND for higher bit density, ultimately enabling SSDs upwards of ~100TB in capacity. The catch is that they are rated at only ~150 write cycles. This is fine for archival storage requiring WORM workloads, and you still maintain NAND speeds when it comes to reading that data later on, meaning that decade old Facebook post will appear in your browser just as quickly as the one you posted ten minutes ago.
Next up was a look at some preliminary Intel Optane SSD results using RocksDB. Compared to a P3600, the prototype Optane part offers impressive gains in Facebook's real-world workload. Throughput jumped by 3x, and latency reduced to 1/10th of its previous value. These are impressive gains given this fairly heavy mixed workload.
More to follow from FMS 2016!