Protecting archives from damage

RAR archive format supports a special type of redundant data called the recovery record. Presence of recovery record makes an archive larger, but allows to repair it even in case of physical data damage due to disk failure or data loss of other kind, provided that the damage is not too severe. Such damage recovery can be done with Repair archive command. ZIP archive format does not support the recovery record.

Set "Add recovery record" option in Archive name and parameters dialog to add the recovery record to archive. Another approach is to enable "Add recovery record" option in the default compression profile. In this case the recovery record will be added to archives after any archive modification.

If you need to add the recovery record in the command line mode, please read descriptions of rr[N] command and -rr[N] switch, which can be used for this purpose.

RAR 5.0 archive format recovery record uses Reed-Solomon error correction codes. In case of a single continuous damage, typically it is possible to restore slightly less data than recovery record size. Recoverable data size can be lower for multiple damages.

You can specify the recovery record size in Advanced options of "Archive name and parameters" dialog as a percent of archive size. Also it can be set in Protect archive command. Larger recovery record allows to restore a larger damaged area, but increases the archive size more and is processed slower. Usually 3 - 10% of archive size is a reasonable choice. Due to service data overhead the actual resulting recovery record size only approximately matches the user defined percent and difference is larger for smaller archives.

To repair a corrupt archive containing the recovery record in WinRAR shell mode, apply "Repair" command to it. In the command line use command "r". The repaired archive will be given the name fixed.arcname.rar, where 'arcname' is the original damaged archive name. If corrupt archive does not contain the recovery record or if archive is not completely recovered due to a major damage, the second stage is performed. During this stage only the archive structure is reconstructed and it is impossible to recover files failing the checksum validation, but it is still possible to recover undamaged files, which were inaccessible due to corrupt archive structure. This is useful mostly for non-solid archives. This stage is not performed for archives with encrypted file names, which can be repaired only if recovery record is present.

When the second stage is completed, the reconstructed archive will be saved as rebuilt.arcname.rar, where 'arcname' is the original archive name.

If a recovery record is partially broken, its remaining valid data still can be utilized to repair files. Repair command does not fix broken blocks in recovery record itself, only file data is corrected. After successful archive repair, you may need to create a new recovery record for rescued files.

While the recovery record improves chances to repair damaged archives, it does not guarantee the successful recovery. Consider combining the recovery record feature with making multiple archive copies to different media for important data.