Opportunistic Log: Efficient Installation Reads in a
Reliable Storage Server
James O'Toole and Liuba Shrira
Laboratory for Computer Science
Massachusetts Institute of Technology
Cambridge, MA 02139
Abstract
In a distributed storage system, client caches managed on the basis of
small granularity objects can provide better memory utilization then
page-based caches. However, object servers, unlike page servers, must
perform additional disk reads. These installation reads are
required to install modified objects onto their corresponding disk
pages. The opportunistic log is a new technique that
significantly reduces the cost of installation reads. It defers the
installation reads, removing them from the modification commit path,
and manages a large pool of pending installation reads that can be
scheduled efficiently.
Using simulations, we show that the opportunistic log substantially
enhances the I/O performance of reliable storage servers. An object
server without the opportunistic log requires much better client
caching to outperform a page server. With an opportunistic log, only
a small client cache improvement suffices.
Our results imply that efficient scheduling of installation reads can
substantially improve the performance of large-scale storage systems
and therefore introduces a new performance tradeoff between page-based
and object-based architectures.
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