Jiajia

Overview

Jiajia is a ScaleFlux engineer who presented a resource grant and isolation design for Flexible Data Placement (FDP). The starting problem: in current FDP all reclaim units share capacity with no overprovision management, which can cause unfair overprovisioning between reclaim unit handles running different traffic patterns. Using a 3.84 TB device example, Jiajia showed an active random-traffic RUH 0 grabbing free space to reach write amplification factor (WAF) around 1.5 and 800k IOPS, then a later sequential RUH 1 — expected to hit WAF around 1 and 10 GB/s — instead degrading because the first RUH consumed too many free blocks.

To fix this, Jiajia proposed a fairly overprovision grant where garbage collection is triggered by per-reclaim-unit space consumption rather than overall free block count (illustrated by splitting the 3.84 TB device into three RUs, e.g. a 0.32 TB RU2 triggering GC near 0.2 TB consumption), making reclaim-unit life more predictable. Jiajia also described prioritized overprovision and mixed media — one RU configured as SLC medium alongside TLC/QLC in a single device, with SLC offering better random read latency, higher PE cycles, and less NAND error for hot or metadata — and extended isolation beyond NAND to other device resources: CPU time via rewrite credit control, SRAM write buffer allocation by priority group, and flash command queues with different queue depths and fetch weights per RUH for more predictable WAF and performance.