How Unrar Handles Multi-Volume Part01 RAR Archives

When dealing with split RAR archives, the unrar utility simplifies the extraction process by automatically detecting, sequencing, and assembling files across multiple segments. When an extraction command targets the first file—typically named with the .part01.rar suffix—the tool reads the archive's internal metadata, verifies the presence of subsequent volumes in the directory, and reconstructs the original files continuously without requiring manual intervention for each individual part.

The Multi-Volume Naming Convention

Modern versions of RAR use a standardized naming convention for split archives:

  • archive.part01.rar (the initial volume)
  • archive.part02.rar (the second volume)
  • archive.part03.rar, and so on.

This system replaced the legacy naming format (which used .rar, .r00, .r01). The .partXX.rar convention makes the exact order of parts immediately identifiable to both the user and the software.

How Extraction Works

To unpack a multi-volume archive, you only need to run the extraction command against the primary volume:

unrar x archive.part01.rar

When this command is executed, unrar performs the following steps:

  1. Header Inspection: The utility checks the header of archive.part01.rar. This header contains flags indicating that the file is part of a multi-volume set, along with details about whether a stored file spans across multiple boundaries.
  2. Sequential Reading: unrar extracts the data stored inside part01.
  3. Automatic Volume Chaining: As soon as the end of part01.rar is reached, unrar automatically searches the current directory for archive.part02.rar. If found, it seamlessly continues reading the stream.
  4. Data Assembly and Integrity Checks: If an individual file within the archive spans across part01 and part02, unrar reconstructs the file without corruption. Once extraction finishes, it verifies the checksums (CRC32 or BLAKE2) to ensure data integrity.

Requirements for Successful Extraction

For unrar to successfully process a .part01.rar archive:

  • Complete Set: All subsequent parts (.part02.rar, .part03.rar, etc.) must be present.
  • Same Directory: By default, all parts must reside in the same folder where the command is executed.
  • Unmodified File Names: The base name and numbering pattern must remain intact. If archive.part02.rar is renamed or missing, unrar halts and prompts the user to specify the path to the missing volume. If the volume cannot be provided, the process terminates with an error.