MultipartArchive

MultipartArchive is a concept describing an archive that is stored or transmitted as multiple discrete files, or volumes, while representing a single logical container. It is commonly used to facilitate transfer over size-limited channels, support long-term backups, or enable distribution across media with finite capacity. The volumes collectively contain all data and metadata needed to reconstruct the original archive.

A multipart archive typically includes an index or manifest that records the number of volumes, their sequence, individual sizes, and integrity checks such as checksums. The volumes are named in a way that indicates order, for example archive.zip with accompanying archive.z01, archive.z02, or archive.001, archive.002, depending on the format and tool. Tools that support multipart archives use the manifest to verify integrity and determine when all parts have been received before extraction.

Formats and implementations vary. Real-world variants include ZIP-based split archives that pair a base file with subsequent .z01, .z02, etc., 7-Zip and RAR multi-volume archives that use sequential part extensions, and other format-specific split conventions. Some systems allow metadata to reference the total number of parts and the expected combined size. Compatibility can differ between tools, so all parts are typically required for successful extraction.

Use cases include distributing large datasets over email or cloud storage with per-file limits, archiving very large collections, and enabling incremental backups across media with fixed capacities. Limitations include the need to manage all volumes together, potential data loss if a single part is missing or corrupted, and reliance on compatibility between the archived data and the extraction tool. Security practices often involve applying encryption to the archive as a whole and protecting the integrity of the part sequence.