This article explains why users with a large number of files, typically in the millions, might experience long incremental backup times.
There are two factors that contribute to longer run times for incremental backups:
- First, the Windows agent scans all files/directories on the specified volumes to determine modification times. Files with modification timestamps more recent than the last successful backup are included in the incremental backup.
- Secondly, the Windows agent also looks at the archive property on each file whose modification timestamp does not meet the first criteria. If the archive property is set, the file is included in the incremental backup.
See About the NTFS Change Journal in the Recovery-Series and UEB Administrator's Guide for ways to change the journal to alleviate this issue.