DAFT: Disk geometry-Aware File system Traversal

Abstract

Bulk file access is a read access to a large number of files in a file system. Example applications that use bulk file access extensively are anti-virus (AV) scanner, file-level data back-up agent, filesystem defragmentation tool, etc. This paper describes the design, implementation, and evaluation of an optimization to modern file systems that is designed to improve the read efficiency of bulk file accesses. The resulting scheme, called DAFT (disk geometry-aware file system traversal), provides a bulk file access application with individual files while fetching these files into memory in a way that respects the disk geometry and thus is as efficient as it can be. We have successfully implemented a fully operational DAFT prototype, and tested it with commercial AV scanners and data back-up agents. Empirical measurements on this prototype demonstrate that it can reduce the elapsed time of enumerating all files in a file system by a factor of 5 to 15 for both fragmented and non-fragmented file systems on fast and slow disks.