Timebox: A high performance archive for split snapshots

Timebox is a novel high-performance snapshot system for object storage systems. The goal is to provide a snapshot service that is efficient enough to permit "back-in-time execution" where read-only programs run against application-specified snapshots. Back-in-time execution allows to answer questions about what happened in the past by performing analysis that is often impossible to perform against rapidly evolving current state because of interference or because the questions are posed in retrospect.; A key innovation in Timebox is that, unlike earlier systems, Timebox supports update-in-place storage systems rather than no-overwriting systems and provides snapshots that are transactionally consistent, yet non-disruptive. It uses novel in-memory data structures to ensure that frequent snapshots do not block applications from accessing the storage system, and do not cause unnecessary disk operations. Timebox takes a novel approach to dealing with snapshot meta-data using a new technique that supports both incremental meta-data creation and efficient meta-data reconstruction.; A basic problem of storing the captured past states over long time scales is how to manage snapshot storage so that important snapshots can be kept for required time, even when archive space becomes limited. Timebox addresses this problem by providing a new capability---selective snapshot reclamation. The application specifies which snapshots are important. When archive space becomes limited, the system reclaims unimportant snapshots retaining the important ones, efficiently. Timebox uses novel snapshot storage management techniques that take advantage of flexible snapshot representation to avoid archive space fragmentation and to maintain efficient access to retained snapshots.; We have implemented a Timebox prototype and analyzed its performance. Experimental results show that providing snapshots for back-in-time activities has low impact on system performance even when snapshots are frequent. Experimental results also show that for expected update workloads, Timebox reclaims selected unwanted snapshots with minimal impact on the storage system.