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Technical Report Details

Date 17-10-2007
Number DISI-TR-07-07
Title The Chunk-Skew Layout
Authors Alessandro Di Marco
Bibtex Entry
E-mail dmr@disi.unige.it
Link ftp://ftp.disi.unige.it/person/DimarcoA/chunkskew.pdf
Abstract In the last couple of years, hard-disk technology has experienced an unjustified progressive boost of the built-in cache size, affecting both the power consumption and the reliability of stored data. Large built-in caches expose to a greater risk of significant data loss in case of power outage with respect to the smaller ones, without offering significant benefits in terms of performance. As a consequence, these caches need to be kept in write-through mode in all those scenarios where data reliability is a matter of primary concern. This implies severe repercussions on the disk write performance, due to the role of the built-in cache itself, mainly acting as a write scheduler, rather than just a mere I/O buffer, as its ever increasing size would suggest. This paper discusses the chunk-skew layout, a novel data layout strategy targeted to improve the performance of commodity hard-disks in mission-critical systems. In this scenario, the proposed layout turned out to be really effective, scoring performance speedup of nearly 300 percent with respect to the usual data layout. Moreover, further performance improvements up to 350 percent speedup are expected following an exact hard-disk characterization. For this purpose we analyzed the differences in terms of geometry and performance in a batch of identical commodity hard-disks, discovering an unexpected and more complex scenario where most of the assumptions made so far on hard-disk technology do not hold anymore.
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