I hope someone is able to answer this question: How does Time machine guarantee a consistent backup of your files, when it comes to libraries (e.g. iPhoto, iTunes etc.) or index files in general ? What I have been thinking about is that, especially during its first backup, the backup process can take quite a while. During this process it can very well be, that some of the files are changed again. Does the very first 'time machine'-backup on a machine represent the state of the file system at the beginning or at the end of that backup - or (hopefully not) does it represent the state of each file at the exact moment that it is backed up ? Wouldn't that mean that, if for example you're installing something big during a time machine backup, you may end up with a backup in which this program is "half-installed" ? Also, what about libraries, where you have an actual index of the files, and also the files themselves (e.g. the iTunes library) - what happens if Time machine has already backed up the index file and is now backing up the individual files, but at this point you delete some of them => the index changes, but may have already been backed up - and is therefore outdated. I do know about FSEvents and some of its inner workings, I just don't know whether time machine uses that information during its backups... I want to believe Apple have thought this through - but I'd really love to get a deeper understanding of this. It also doesn't inspire confidence that Apple themselves warn against backing up Aperture libraries due to consistency issues... Thanks in advance, guys !