time machine on two drives
I've searched here and on the wider web and am in search of some clarification.
I want to set up 2 usb/firewire exterenal drives on my wife's iMac and use them exclusively for Time Machine. What I'd like to have happen is for Time Machine to see both drives and make backups of the iMac to each drive automagically.
I've seen posts that say 'sure, you can do this' and others that say 'you have to add the 2nd drive in TM, plug in one and only one drive, have TM do the the backup, then unplug the drive, add the 2nd, and have TM backup to that drive'.
I don't want to buy a 2nd drive until I understand the mechanics of doing the TM backup to 2 different external drives on one iMac.
Thank you for your help.