I can always mount it later if I need it, correct?
You could mount it, but not run from it.
I'd Partition the external into at least two for the OSX drives & clone With Carbon Copy Cloner.
What's the best way to back up files without interrupting the library directory system? In other words, itunes and iphoto will be asking me where are my **** files?
Cloning or backing up won't confuse it, but are you talking about Moving them?
I thought SP would throw everything together to the external drive.
That's bad enough with OS and files on one drive, but mix files from several drives..... what a mess.
It's also a directory nightmare, which is likely why no software that I know of does that.
One backup volume per one source volume, clone,TM or otherwise, that is how a backup is (should be) done.
If it's just files that you want, drag and drop copy to another volume is fine.
If you want to retain resource forks to the software that created each file, and (especially) if you want bootability, use a clone utility like SuperDuper.
To save time after the initial backup, use Smart Update of SuperDuper.
BUT, DO have one volume for each volume that you wish to backup.
how many drives do you have running?
Currently have 6 machines and a total of 21 drives running.
In two machines I use TM and SD! backup, in the other four I use SD! only.
I've never fallen back/used a TM backup, but constantly use SD! backups.
The performance benefit of running a SD! clone is one main reason.
When would it be appropriate to run SP or CCC?
I run the initial SD! clone upon setup of a drive.
After that, I base frequency on the usage.
With full time machines, Smart Update of SD! runs every night.
In other machines, I run Smart Update once a week.
Having so many drives, it can get hard to cover backups drive for drive, but 1:1 is a better backup scheme.
With the 1TB, 2 TB and 3 TB drives getting so reasonable, a single drive can be partitioned to serve as backup for two, three or even four volumes.
Of course, it is better to limit the number of volumes on a single drive in case of catastrophy....