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USENIX 2002 Annual Conference - Technical Program Abstract
Bridging the Information Gap in Storage Protocol Stacks
Timothy E. Denehy, Andrea C. Arpaci-Dusseau, and Remzi H. Arpaci-Dusseau,
Department of Computer Sciences, University of Wisconsin, Madison
Abstract
The functionality and performance innovations in file systems and
storage systems have proceeded largely independently from each other over the
past years. The result is an information gap: neither has information
about how the other is designed or implemented, which can result in a high
cost of maintenance, poor performance, duplication of features, and
limitations on functionality. To bridge this gap, we introduce and evaluate a
new division of labor between the storage system and the file system. We
develop an enhanced storage layer known as Exposed RAID (ExRAID), which
reveals information to file systems built above; specifically, ExRAID exports
the parallelism and failure-isolation boundaries of the storage layer, and
tracks performance and failure characteristics on a fine-grained basis. To
take advantage of the information made available by ExRAID, we develop an
Informed Log-Structured File System (I.LFS). I.LFS is an extension of the
standard log-structured file system (LFS) that has been altered to take
advantage of the performance and failure information exposed by
ExRAID. Experiments reveal that our prototype implementation yields benefits
in the management, flexibility, reliability, and performance of the storage
system, with only a small increase in file system complexity. For example,
I.LFS/ExRAID can incorporate new disks into the system on-the-fly, dynamically
balance workloads across the disks of the system, allow for user control of
file replication, and delay replication of files for increased
performance. Much of this functionality would be difficult or impossible to
implement with the traditional division of labor between file systems and
storage.
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