Date Added: Jan 2010
A new generation of storage systems exploits decreasing storage costs to allow applications to take snapshots of past states and retain them for long durations. Over time, current snapshot techniques can produce large volumes of snapshots. Indiscriminately keeping all snapshots accessible is impractical, even if raw disk storage is cheap, because administering such large-volume storage is expensive over a long duration. Moreover, not all snapshots are equally valuable. Thresher is a new snapshot storage management system, based on novel copy-on-write snapshot techniques, that is the first to provide applications the ability to discriminate among snapshots efficiently. Valuable snapshots can remain accessible or stored with faster access while less valuable snapshots are discarded or moved off-line.