Unrar Missing Volume: What Happens During Extraction

When attempting to extract a multi-volume RAR archive without all required parts, the unrar utility cannot complete the extraction process. This guide explains how unrar detects missing split files, the specific errors generated during execution, what happens to partially extracted data, and the methods available to salvage files from an incomplete archive set.

The Immediate Behavior of `unrar`

When unrar begins extracting a multi-volume archive (such as .part1.rar, .part2.rar, or legacy .rar, .r00, .r01 files), it reads the headers to determine the total sequence of parts. If an intermediate or subsequent volume is absent from the target directory, extraction stops the moment the missing data is required.

Depending on the environment, the tool reacts in one of two ways:

Interactive Mode: If run in a standard terminal without automated flags, unrar pauses and prompts the user to insert the missing volume or enter the full path to the required file.
Non-Interactive Mode: In automated scripts or when flags like -y (assume yes) are passed, the process immediately aborts and outputs an error message, typically:
```
Cannot find the volume: archive.part2.rar
Corrupt file or wrong password
Total errors: 1
```

What Happens to the Extracted Files?

The state of the output files depends entirely on where each file is located within the archive structure:

1. Files Contained Completely in Earlier Volumes

Any file that begins and ends inside the volumes processed prior to the missing file will extract normally and remain fully functional on your disk.

2. Files Spanned Across the Missing Volume

If a single file spans across the boundary into the missing volume, unrar cannot complete the reconstruction. By default, unrar automatically deletes this incomplete, corrupted file upon terminating the process to prevent damaged data from remaining in your filesystem.

3. Files Located in Subsequent Volumes

Any files stored entirely in later parts of the archive will not be processed at all. Because unrar terminates execution when the sequence breaks, it does not scan ahead to extract independent files located in later volumes.

How to Keep Partial Data

If an extraction fails due to a missing volume, you can force unrar to retain whatever data it managed to extract before the failure by using the Keep Broken flag (-kb):

unrar x -kb archive.part1.rar

With the -kb switch enabled, unrar will not delete the partially extracted file when the process aborts. This is particularly useful for multimedia files (such as video or audio streams) that can often be partially played even if the tail end of the data stream is missing.

Resolving Missing Volume Errors

If you encounter this error, consider the following fixes:

Verify Filename Consistency: Ensure all volumes follow identical naming conventions (e.g., data.part1.rar, data.part2.rar). A single typo will cause unrar to assume the volume is missing.
Utilize Recovery Volumes (.rev): If the archive was created with parity recovery volumes, locate the .rev files. If you have enough .rev files to match the number of missing RAR volumes, double-clicking or running unrar on any .rev file will reconstruct the missing .rar parts.
Locate the True Missing Part: Because RAR multi-volume archives rely on contiguous data streams across volume boundaries, locating and downloading the exact missing segment is the only way to ensure 100% data integrity for all contained files.