MAPL : Move-anywhere proximate layout

MAPL is a journaling file system providing advanced data management features like snapshots and clones. It is also designed to show read/write performance near that of raw disk access for both random and sequential access patterns. Further, the system is designed to show stable I/O performance over time, regardless of the workload placed on it. Important goals of the design are that MAPL seeks to make I/O to the active file system behave like I/O to a LUN on a hardware-based RAID array, while minimizing performance overhead caused by snapshots. Specifically, MAPL minimizes the effects on write activity of snapshot creation, as well as the effects of the presence of snapshots on ongoing I/O. Like the frame arrays it mimics, MAPL is optimized for large files, and its performance goals center on them.