Use snapshot for open files

How to work around files that are open when you backup.

With just normal operations, open files are easily handled. You try to copy from point a to point b, and you get the "cannot copy" message from your Windows OS saying that the file is in use, so with a muttered imprecation, you close the file and try again. But with enterprise wide backups, it's a bit more serious. In fact, an open file can scrub your backup, and even cause data corruption that you don't know about until you test your...

recovery procedures, or, heaven forbid, you really have to use some backed up files, and they're not ready for prime time.

According to a white paper on the Veritas Web site, open files are the cause of some 97 percent of incomplete backups. And it's more and more likely that you'll have open files when you start backing up, because the window for performing backups is shrinking even as you're reading this.

Clearly you need a solution that will allow you to deal with those open files. Various vendors provide this, but the solution may not be the default when you're doing your backups, so you should either make sure to enable such an option in the software you're using, or at least understand what the downside is of not using such an option. The ability to deal with open files during a backup operation, often referred to as a writer, ensures that if a file is changed, the data as it existed at the beginning of the backup operation is the data that is kept in the backup file. This is accomplished through a process of taking a snapshot of the original file as of the onset of backup, and then comparing it with the data as the backup operation proceeds, selecting the data that is consistent for inclusion in the backup.

The Veritas white paper contains a detailed description of such a process.


David Gabel is the executive technology of TechTarget.


This was first published in June 2003

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