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SOSP PRACTICE TALK-FS2: Dynamic Data Replication in Free Disk Space for Improving Disk Performance and Energy-Consumption


Disk performance is increasingly limited by its head positioning latencies, i.e., seek time and rotational delay. To reduce the head positioning latencies, we propose a novel technique that dynamically places copies of data in file system's free blocks according to the disk access patterns observed at runtime. As one or more replicas can now be accessed in addition to their original data block, choosing the "nearest" replica that provides fastest access can significantly improve performance for disk I/O operations.

We implemented and evaluated a prototype based on the
popular Ext2 file system. In our prototype, since the file system layout is modified only by using the free/unused disk space (hence the name Free Space File System, or FS2), users are completely oblivious to how the file system layout is modified in the background; they will only notice performance improvements over time. For a wide range of workloads running under Linux, FS2 is shown to reduce disk access time by 41–68% (as a result of a 37–78% shorter seek time and a 31–68% shorter rotational delay) making a 16–34% overall user-perceived performance improvement. The reduced disk access time also leads to a 40–71% energy savings per access.

Hai Huang is a Ph.D. student working with Prof. Kang G. Shin
at Real-Time Computing Lab. His research interests are in low-power systems, file and storage systems, operating systems, and real-time systems. He received his B.S. in Computer Science and Engineering at the Ohio State University in 2000, M.S. in CSE at the University of Michigan in 2002. He is expecting to graduate and receive a Ph.D. degree in CSE in 2006.

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