PAST (PDB Archival Snapshot Toolkit) allows users to create date-stamped mirrors of the current PDB repository, and it maintains all previous archives using an efficient storage mechanism. Although the PDB development team now provides archival copies of the PDB for selected dates, the archives are infrequent (updated yearly) and do not provide an efficient means of storing the redundant data. PAST is based on an efficient indexing technique similar to the ones used by Picasa and iTunes. We only store one physical copy for each unique file. PAST archival snapshots precisely mirror the directory structure and files in the PDB, but all files in the snapshot directory are replaced by links to a minimal set of data to prevent wasteful use of space. PAST has been tested and deployed in our lab to create weekly PDB snapshots corresponding to ASTEROIDS releases.
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