In each of a number of passes to deduplicate a data object, a transaction is started. Where an offset into the object has previously been set, the offset is retrieved; otherwise, the offset is set to reference a beginning of the object. A portion of the object beginning at the offset is deduplicated until an end-of-transaction criterion has been satisfied. The transaction is ended to commit deduplication; where the object has not yet been completely deduplicated, the offset is moved just past where deduplication has already occurred. The object is locked during each pass; other processes cannot access the object during each pass, but can access the object between passes. Each pass is relatively short, so the length of time in which the object is inaccessible is relatively short. By comparison, deduplicating an object within a single pass prevents other processes from accessing the object for a longer time.