The time that is required to perform a restore from a synthetic backup does not increase significantly over time.

The restore times for both a complete synthetic backup and for a single file is the same. It is the same whether the restore is from a traditional backup or from a synthetic backup.

The restore time of a single directory may increase over time when sourced from synthetic backups. The restore time depends on the pattern of file changes within the directory.

Contrast a traditional full backup, which stores the files in file system order with a synthetic full backup, which stores the files in last-file-accessed order. The synthetic full contains the newest files at the front of the media and the unchanged files at the end. Over time, the processing order introduces the potential for fragmentation of a single directory across the synthetic full image.

Note that the scenario is limited to single directory restores. Single file restores and full image restores from synthetic fulls are equal or better than from traditional full backups, as noted in previous bullets.