disk utility question

[dtrapp]

How do you use the disk utility in 12.04 to scan the file system? I would like to scan the filesystem on a mounted drive but when I click on the Check Filesystem button I get the message that the disk is busy. Is there a set of instructions for this utility?

[black veils]

backup your data first.

you need to do this from a live cd/dvd/usb stick.

[dtrapp]

Thanks