Take the tour ×  So I got a USB drive I want to use with Time
Machine. This USB drive has some files of mine.  If Time Machine
creates the backup in it, what happens to such files? Are they
deleted?  share|improve this question add comment  2 Answers  up
vote 4 down vote accepted  Two things happen:    1. Time Machine
sees if the format is acceptable and makes a change to enforce
enhanced security on that drive if needed.   2. Time Machine
makes a folder named Backups.backupdb if needed and makes a
folder for each machine that uses that drive.  Assuming you
don't have a Backups.backupdb folder - then everything on the
drive won't be touched by Time Machine. If the drive isn't in a
mac format, you may be asked to erase the drive and reformat it.
Do use care and read any messages carefully before you start
that first backup.  Full details on this is at
http://support.apple.com/kb/HT1427 - look for the section titled
Changing your backup disk about a quarter of the way down for
the restrictions on which format d