4th USENIX Conference on File and Storage TechnologiesAbstract
Pp. 337350 of the Proceedings
Accurate and Efficient Replaying of File System Traces
Nikolai Joukov, Timothy Wong, and Erez Zadok, Stony Brook University
Replaying traces is a time-honored method for benchmarking,
stress-testing, and debugging systemsand
more recentlyforensic analysis. One benefit to replaying
traces is the reproducibility of the exact set of operations
that were captured during a specific workload.
Existing trace capture and replay systems operate at different
levels: network packets, disk device drivers, network
file systems, or system calls. System call replayers
miss memory-mapped operations and cannot replay I/Ointensive
workloads at original speeds. Traces captured
at other levels miss vital information that is available only
at the file system level.
We designed and implemented Replayfs, the first system
for replaying file system traces at the VFS level.
The VFS is the most appropriate level for replaying file
system traces because all operations are reproduced in a
manner that is most relevant to file-system developers.
Thanks to the uniform VFS API, traces can be replayed
transparently onto any existing file system, even a different
one than the one originally traced, without modifying
existing file systems. Replayfs's user-level compiler
prepares a trace to be replayed efficiently in the kernel
where multiple kernel threads prefetch and schedule the
replay of file system operations precisely and efficiently.
These techniques allow us to replay I/O-intensive traces
at different speeds, and even accelerate them on the same
hardware that the trace was captured on originally.
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