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UBC Theses and Dissertations

RSnap : resursive writable snapshots for logical volumes Gupta, Abhishek


Volume Snapshots provide instantaneous checkpoints of a complete filesystem. Whereas previous work on developing snapshot utilities has focused on satiating the need for online backups, modern trends encourage their deployment in expedited clone construction scenarios. Unlike their read-only counterparts, these clones are expected to be mutable and to some extent independent of their base images. We present RSnap, a volume manager that allows users to create mutable recursive snapshots of logical volumes. Storage is allocated to these snapshots in a Dedicate-on-Write fashion. Since unrestrained clone creation can quickly obscure sharing relationships between a set of volumes, RSnap includes an automatic garbage collector that can identify and reclaim unreferenced blocks. RSnap uses the radix tree data structure to implement recursive snap shots. We capitalize on kernel infrastructure to overcome some of the performance and consistency problems in using the radix tree. Our evaluations show that an in kernel radix tree implementation gives satisfactory performance and scales with the number of snapshots.

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