Is there an equivalent of a differential backup for UNIX systems? For a differential to occur on a Windows system, the backup software relies on an archive bit being set when a file is modified but not being reset by the backup software as an incremental backup would behave.
Most commercial backup software products support differential backup on all platforms. It's based on modification times, which is a far more reliable way than the Windows archive bit. The problem with the archive bit is that it gets set or unset whenever ANYTHING backs up a file. That means that if you made your own NTBACKUP of your home directory, the archive bit is set. If your backup software uses the archive bit, it wouldn't back that file up that night. That's just wrong. Backup software should use mtime, not the archive bit.
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This was first published in August 2002