I currently have my 30+GB iTunes library on my external hard drive, however I am constantly updating my library i.e. adding new music, deleting artists I no longer listen to, etc. How can I update my backup without just rewriting the massive folder over and over again? Thanks MR!
Use Time Machine. Apple's built-in incremental backup strategy. Get an external, select it for use with TM, and off you go.
TM will make a copy of your entire drive, and then every hour will add only those files that have changed. The cool bit is that it presents each snapshot to you as all your files, not just the ones that have changed. It does this by using "aliases" to the unchanged files. The TM app can then show you every version of every file that it has, and you can flick through "time" in a very natty interface.
It's free; it's automatic; it does exactly what you want. It will backup all your files, so you need never worry about whether a file in backed up, and you won't need to do manual archives.
Most System files are read-only, so they are only copied once. You will see lots of threads here of people saying "I accidentally deleted my Mail app: do I have to reinstall the OS?". With TM, you just restore the app.
