ZoneAlloy: Elastic Data and Space Management for Hybrid SMR Drives

The emergence of Hybrid Shingled Magnetic Recording (H-SMR) allows dynamic conversion of the recording format between Conventional Magnetic Recording (CMR) and SMR on a single disk drive. H-SMR is promising for its ability to manage the performance/capacity trade-off on the disk platters and to adaptively support different application scenarios in large-scale storage systems. However, there is little research on how to efficiently manage data and space in such H-SMR drives.

In this paper, we present ZoneAlloy, an elastic data and space management scheme for H-SMR drives, to explore the benefit of using such drives. ZoneAlloy initially allocates CMR space for the application and then gradually converts the disk format from CMR to SMR to create more space for the application. ZoneAlloy controls the overhead of the format conversion on the application I/O with our quantized migration mechanism. When data is stored in an SMR area, ZoneAlloy reduces the SMR update overhead using H-Buffer and Zone-Swap. H-Buffer is a small host-controlled CMR space that absorbs the SMR updates and migrates those updates back to the SMR space in batches to bring down the SMR update cost. Zone-Swap dynamically swaps ``hot'' data from the SMR space to the CMR space to further alleviate the SMR update problem. Evaluation results based on MSR-Cambridge traces demonstrate that ZoneAlloy can reduce the average I/O latency and limit the performance degradation of the application I/O during format conversion.