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USENIX Technical Program - Abstract - 13th Systems Administration Conference - LISA '99

Moving Large Filesystems On-Line, Including Exiting HSM Filesystems

Vincent Cordrey, Doug Freyburger, Jordan Schwartz, and Liza Weissler, Collective Technologies


Since the advent of Logical Volume Managers [LVM], larger individual disk drives, and high uptime expectations, it is no longer possible at some sites to schedule downtime windows long enough to move some very large or very critical filesystems to new hardware. Hierarchical Storage Management [HSM] systems share this problem. While at some sites, users continue to enjoy the functionality of HSM based on their specific usage patterns, sites whose usage patterns do not match HSM's strengths have a more acute case of the same problem when moving their data to new hardware. This paper presents a unique approach to moving filesystems that permits a system to remain on-line and accessible. New terminology is also introduced to assist discussion: Forward Relocation, Reverse Relocation, and Hybrid Relocation are defined and basic algorithms are presented. While it is true that the total throughput rate of a traditional dump and restore is higher, the methods presented here require nearly zero downtime.

The authors have used these techniques to relocate data on filesystems with many small files during the working day at several sites, as well as to exit HSM systems as part of standard technology refresh programs. Three case studies, where both types of data were relocated, are described in their basic detail as successful (and ongoing) implementations. The authors know of no prior works on this topic and hope to foster further discussion and refinement of the techniques.

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