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Seminaire MASCOTTE
Corral: Block level versioning device for Linux

par Julian Monteiro


Date :20/05/08
Location :Salle du Conseil


A very promising feature of modern file systems is the ability to maintain multiple versions of the stored data. A possible way to keep all this information is to perform periodic snapshots of the system. The copy-on-write (CoW) method tends to be an efficient way to manage and maintain these snapshots during time.

Based on these techniques we propose the Corral system: a virtual block-device with transparent versioning, which uses the linux device-mapper snapshot as a lower layer. The snapshot method uses a CoW technique to avoid duplicating unchanged blocks betwwen successive versions. As long as the data remains the same, no duplication is done. The Corral system can be used with any file system and can be implemented without the need of a kernel or module recompile.

This system provides an efficient way to maintain a consistent list of modified blocks between version freezes, which can be used by a distributed storage system. Some experiments were done to measure the effectiveness of the proposed system.

This is joint work with Olivier Dalle



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