Garbage Collection Does Not Only Collect Garbage: Piggybacking-Style Defragmentation for Deduplicated Backup Storage

Deduplication is widely used in backup storage and reduces storage overhead by allowing backups to share common data chunks. However, it naturally disrupts the sequential layout of backup images, leading to fragmentation, which slows down backup restoration. Existing solutions to this issue often come with trade-offs, either reducing deduplication effectiveness or introducing significant I/O overhead.