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Hi all this page has a message which goes like this:

If the disk is already in exclusive use by another program or is formatted using a file system other than NTFS file system, FAT, or FAT32, it can't be defragmented.

I was wondering what does it mean for a disk to be in exclusive use by a program?

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They are some software that can manage directly a hard disk. For example, Oracle Data Base Management System can work with raw devices.

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How does a disk identify itself as being "exclusively used" by a program? – Pacerier Dec 15 '11 at 11:23

Other disk management tools can obtain an exclusive lock on a particular drive. For example, if you are using a third party or other Windows utility to defragment or repair a drive already, then Windows defrag utility would not be able to get the exclusive lock that it needs in order to defragment the drive.

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right! take a look to truecrypt troubleshooting: "The operating system reports to TrueCrypt that the device is locked for an exclusive access by an application.Possible Solution: It usually helps to disable or uninstall the interfering application, which is usually an anti-virus utility, a disk management application, etc." – danihp Dec 20 '11 at 22:42

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