[talks] W Josephson preFPO

Melissa Lawson mml at CS.Princeton.EDU
Tue May 18 09:27:51 EDT 2010

William Josephson will present his preFPO on Tuesday May 25 at 1:30PM in Room 402.
The members of his committee are:  Kai Li, advisor; Brian Kernighan and Jen Rexford, 
readers; Mike Freedman and Doug Clark, nonreaders.  Everyone is invited to attend his 
talk.  His abstract follows below.

Title: Rethinking The Storage Software Stack for Flash Memory

Flash memory has recently emerged as an important component of the
storage infrastructure in the data center, but presents several
unique challenges to storage system designers: individual blocks
must be erased before they can be rewritten, block erasure is time
consuming, and individual blocks may be erased only a limited number
of times.  By combining hardware parallelism and a log-structured
approach, state of the art flash storage systems can deliver two
to three orders of mangitude more I/O operations per second than
existing high-performance fibre channel disk drives.  Despite the
emergence of state of the art solid state disks, the storage software
stack has changed little and is still optimized for magnetic disks;
the basic abstraction remains a linear array of fix-sized blocks
together with a very large DRAM cache to convert user I/O to a
smaller number of large I/O transfers.

In this talk, we first examine the impact SSDs have had on the
utility of the buffer cache.  As SSD performance and density improves,
the value of very large DRAM based buffer caches declines.  We
examine the change in tradeoffs through database buffer cache traces
and simulation and offer some simple heuristics to take advantage
of these changes.  Second, we propose a richer interface more
suitable for solid-state storage systems.  This interface provides
for sparse block or object-based allocation, atomic multi-block
updates, and a block discard interface to facilitate reclamation
of unused storage.  Finally, we present DFS, a file system designed
specifically for next generation flash memory systems that takes
advantage of our proposed storage interface.  The result is a
much-simplified file system implementation that runs under Linux.
In both micro- and application benchmarks DFS shows consistent
improvement over ext3 both in throughput and in CPU usage.  For
direct access DFS delivers as much as a 20% performance improvement
in microbenchmarks.  On an application level benchmark, DFS outperforms
ext3 by 7 to 250% while requiring less CPU power.

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