Can TimeMachine backup files that are ON an external disk?

[OCDMacGeek]

I keep my iTunes folder on an external drive, because it is too big to keep on my Mac mini's drive, and I really cannot afford to ever lose these files. Is there any way to set up TimeMachine to actually backup these files (which are on an external disk) to a different external disk?

Thanks for your help.

 

[drlunanerd]

Yes, this should work. Attach the drive you want to backup, then in Time Machine preferences, click on Options.. set it to *not* exclude the drive by removing it with the minus button.

I tried this and it started the backup process. Annoyingly though it stopped and prompted me saying there wasn't enough free disk space on the second external drive I was backing up to, when there was 30GB more than was needed. Time Machine seems to overcompensate when calculating space requirements - I checked the system log and sure enough it's erroneously reporting this.