TrackLace: Data Management for Interlaced Magnetic Recording

Abstract

Interlaced Magnetic Recording (IMR) is a promising technology which achieves higher data density and lower write amplification (WA) than Shingled Magnetic Recording (SMR). In IMR, top tracks and bottom tracks are interlaced so each bottom track is partially overlapped with two adjacent top tracks. Top tracks can be updated without any WA, but bottom track updates require reading and rewriting of affected valid data on the two neighboring top tracks. There are few published studies discussing WA in IMR drives. We propose TrackLace to reduce WA for IMR. TrackLace consists of three techniques: Z-Alloc allocates user data to the tracks in alternating directions and spreads unallocated tracks among allocated tracks; Top-Buffer opportunistically utilizes unallocated top tracks to buffer bottom track updates; and Block-Swap progressively swaps bottom track hot data with top track cold data during high space utilization. To further optimize TrackLace performance, we propose a virtual frame design that can keep the relocated block (due to Top-Buffer or Block-Swap) close to its original location and an adaptive buffering mechanism that can avoid unnecessary redirections depending on the write locality. Evaluations show that TrackLace can reduce WA by 45 percent and lower average latency by 31percent compared with baseline schemes.