Instant Snapshots in a Federated Array of Bricks
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Overview: Snapshot is a fundamental requirement on mid to high end storage systems. An efficient distributed snapshot algorithm that can make the snapshot operations transparent to applications is needed in FAB. This white paper proposes an algorithm, which avoids pausing or aborting write requests by the novel use of a tentative data structure during the two phases commit of a snapshot creation. Read-only operations on snapshots are optimized in common cases, only requiring communications to a small subset of the bricks, in particular, a single replica set or three bricks in FAB.