Data Management and Layout for Shingled Magnetic Recording

Ultimately the performance and success of a shingled write disk (SWD) will be determined by more than the physical hardware realized, but will depend on the data layouts employed, the workloads experienced, and the architecture of the overall system, including the level of interfaces provided by the devices to higher levels of system software. While we discuss several alternative layouts for use with SWD, we also discuss the dramatic implications of observed workloads. Example data access traces demonstrate the surprising stability of written device blocks, with a small fraction requiring multiple updates (the problematic operation for a shingled-write device). Specifically, we discuss how general purpose workloads can show that more than 93% of device blocks can remain unchanged over a day, and that for more specialized workloads less than 0.5% of a shingled-write disk's capacity would be needed to hold randomly updated blocks. We further demonstrate how different approaches to data layout can alternatively improve or reduce the performance of a shingled-write device in comparison to the performance of a traditional non-shingled device.