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PC Hardware in a Nutshell, Second Edition by Barbara Fritchman Thompson, Robert Bruce Thompson

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Developing a Backup Strategy

This is a hardware book, so we don’t spend much time on software. But, in our experience, many people who buy a tape drive have no idea how to use it effectively. We won’t try to explain how to use your backup software, because the specifics vary and nearly any software bundled with a tape drive is sufficient for the task, but we will devote some space to explaining how to get the most from your tape drive and backup software.

File Attributes and the Archive Bit

If you have a tape drive large enough to back up your entire hard disk and the time necessary to use only complete backups, the status of any particular file doesn’t matter. Every file gets backed up every time, whether it was created that day or has been sitting unchanged for a year. But if you need to use some combination of complete and partial backups, the status of each file becomes critical. If a file is unchanged since the last complete backup, you want to ignore it when doing partial backups. If the file was created or changed since the last complete backup, it needs to be copied to the partial backup tape.

All modern operating systems maintain a file attribute for each file called the archive bit . When a file is created or changed, the operating system toggles the archive bit on, indicating that that file is a candidate for backup. Backup software can manipulate the archive bit, either turning it off after it backs up the file, or leaving it on so that file will again be backed up ...

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