Hello there Long story short I may be using my Mac's external USB drive, temporarily, for another purpose and will be moving the files off it to empty the drive. Once I'm done, I'll be putting the files back on the drive EXACTLY the same as before. However, because the 'modified' or 'last changed' date on the files will have changed because they've been moved- the next time Time Machine runs it'll want to back-up everything all over again won't it? Even though the files are the same, some of the Metadata will be altered and so TM'll back those up from scratch I suspect? Thanks for any advice- I'm 90% certain that'll be how it works but haven't been able to find a definitive answer.