DATE: Thursday , December 13, 2001
TIME: Noon - 1 pm
PLACE: Wean Hall 8220

Jiri Schindler
Carnegie Mellon University

Track-Aligned Extents: Matching Access Patterns to Disk Drive Characteristics

While state-of-the-art disk drives can deliver tens of MBs of data per second, operating systems are capable of utilizing only a small fraction of the available bandwidth. This mismatch is caused by a high-level interface between the storage and the operating systems, which does not reveal disk drive strengths.

This talk will describe a method for matching access patterns to disk characteristics, called traxtents, the the benefits to video servers and file systems. By allocating and accessing data in track-sized extents that are aligned on track boundaries, traxtents can achieve 50% larger efficiency resulting in 1/3 shorter response times. In video servers, track-aligned access yields much smaller response time variance compared to traditional (track-unaligned) access methods, resulting in reduced buffer-space requirements and lower startup latencies for video streams. Even though traxtents utilize disk characteristics, a file system does not use any disk-specific information, but treats track boundary information merely as hints ensuring proper operation on all disks, as demonstrated by an implementation of traxtents in FreeBSD's Fast File System.

Jiri Schindler is fourth-year graduate student at Carnegie Mellon's Parallel Data Laboratory working under Prof. Greg Ganger. His research areas include file and storage systems. Recently, he has been working on disk characterization, timing-accurate storage emulation, and freeblock scheduling inside device drivers.

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