How 7-Zip Handles Missing Split Volume Parts

7-Zip requires all parts of a split multi-volume archive to be present and undamaged to guarantee a complete extraction. When dealing with corrupt or missing split volumes—such as .7z.001, .part1.rar, or .z01 files—7-Zip strictly enforces data integrity checks. This article explains how 7-Zip detects missing or broken archive segments, the difference in handling between solid and non-solid compression, and the limitations of recovering partial data.

The Role of Archive Headers

To open or list the contents of a split archive, 7-Zip requires the volume containing the main archive header. In formats like 7z and RAR, this metadata is typically stored in the first volume (e.g., .001 or .part1.rar) or the last volume.

If the volume containing the archive header is missing or corrupted:

  • 7-Zip will display an error such as "Cannot open file as archive."
  • The program cannot read the file directory, file names, or file sizes, preventing extraction entirely.

If the header volume is intact but subsequent volumes are missing:

  • 7-Zip can open the archive and display the full file list.
  • Extraction will proceed normally until the decompressor requests data residing on a missing or corrupt segment.

Solid vs. Non-Solid Archives

The extraction behavior heavily depends on whether the multi-volume archive was compressed using "solid" mode.

  • Solid Archives (Default for .7z): In a solid archive, all files are packed into a single, continuous data stream before being split into separate volumes. If any volume is missing or corrupted, 7-Zip cannot decompress the stream past the point of corruption. Any files positioned after the damaged or missing section in the stream cannot be extracted, even if the subsequent volumes are intact.
  • Non-Solid Archives: In non-solid mode, each file is compressed independently. If a volume is missing, 7-Zip can still successfully extract files that are entirely contained within the intact volumes. However, any individual file that physically spans across the split boundary into a missing volume will fail extraction.

Error Messages Generated by 7-Zip

When 7-Zip encounters a broken or missing part during the extraction process, it halts the operation and displays one of several standard errors:

  • Unexpected End of Data: Occurs when the next sequential volume is completely missing from the directory.
  • Data Error: Occurs when a split part exists, but the compressed data inside is altered, truncated, or corrupt.
  • CRC Failed: Occurs after extraction when the computed checksum of the unpacked file does not match the checksum recorded in the header.

Recovery Capabilities

7-Zip does not natively support built-in error recovery records for the .7z format. Unlike RAR archives that may contain dedicated parity recovery records, 7-Zip cannot rebuild missing data chunks on its own.

When extraction fails on a corrupt or missing split file, 7-Zip typically deletes the incomplete output file from the destination folder by default. Users attempting to salvage partial data from non-solid archives must explicitly configure the extraction settings to keep broken files, or utilize command-line options such as -bb0 combined with extraction attempts on isolated individual files.