Hello, I do the same thing. I have a TM drive at home and one at work. Time Machine is perfectly capable of using multiple disks, HOWEVER, normally, you have to enter the System Preferences and change the Time Machine disk anytime you hook up a new one (e.g. so when you get to the office and hook up the work drive, you would have to select 'Change Disk' in the TM section of the System Preferences, and then have to do it again when you get home and hook up the home TM drive). Me, always looking to streamline, did some research online, and found that some grand soul had already figured it out.
Here is what I do to make this work. When formatting each drive, I give them a unique name (e.g. Home Time Machine, and Work Time Machine).
Here is the script I found online during my search for this answer, but in order to use it, you need to enable 'GUI Scripting'. Open the 'AppleScript Utility' on your system and check enable GUI scripting.
Open 'Script Editor' on your system and paste this into it (between, but not including the dashed lines!):
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set primarydrivename to "Home Time Machine"
set secondarydrivename to "Work Time Machine"
register_growl()
activate application "System Preferences"
tell application "System Events"
tell process "System Preferences"
click menu item "Show All Preferences" of menu 1 of menu bar item "View" of menu bar 1
click button "Time Machine" of scroll area 1 of window "System Preferences"
repeat until exists window "Time Machine"
delay 0.2
end repeat
click button 1 of group 1 of window "Time Machine" -- change disk
(* If primary disk is mounted switch to it, otherwise switch to secondary disk *)
repeat until exists sheet 1 of window "Time Machine"
delay 0.2
end repeat
set tablecontents to (rows of table 1 of scroll area 1 of sheet 1 of window "Time Machine")
set rownumber to 0
set primarydriveavailable to false
repeat with tablerow in tablecontents
set rownumber to rownumber + 1
set volumename to value of static text of row rownumber of table 1 of scroll area 1 of sheet 1 of window "Time Machine"
log volumename
if volumename as string is primarydrivename then
set primarydriverownumber to rownumber
set primarydriveavailable to true
else if volumename as string is secondarydrivename then
set secondarydriverownumber to rownumber
end if
end repeat
try
if primarydriveavailable is true then
set desiredrownumber to primarydriverownumber
else
set desiredrownumber to secondarydriverownumber
end if
set volumename to value of static text of row desiredrownumber of table 1 of scroll area 1 of sheet 1 of window "Time Machine"
select row desiredrownumber of table 1 of scroll area 1 of sheet 1 of window "Time Machine"
click button "Use for Backup" of sheet 1 of window "Time Machine"
set message to "Time Machine has ben set to backup to " & volumename
my growlnote("General Notification", message)
on error
set message to "Time Machine preferences were not changed"
my growlnote("error notification", message)
end try
delay 1 -- wait for a confirmation dialog that appears if you select a partition on the same physical disk as that being backed up
if (exists button "Use Selected Disk" of window 1) then
click button "Use Selected Disk" of window 1
end if
click menu item "Quit System Preferences" of menu 1 of menu bar item "System Preferences" of menu bar 1
end tell
end tell
on register_growl()
try
tell application "GrowlHelperApp"
set the allNotificationsList to {"General Notification", "Debug Notification", "Error Notification"}
set the enabledNotificationsList to {"General Notification", "Debug Notification", "Error Notification"}
register as application "Configure TimeMachine" all notifications allNotificationsList default notifications enabledNotificationsList icon of application "TimeMachine"
end tell
end try
end register_growl
on growlnote(growltype, str)
try
tell application "GrowlHelperApp"
notify with name growltype title growltype description str application name "Configure TimeMachine"
end tell
end try
end growlnote
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In the script above, change each instance of 'Home Time Machine' and 'Work Time Machine' to the respective names of your two TM drives. Save the altered script with 'File>Save As...' and choose a filename, while also choosing the 'Application' file format.
Lastly, download 'Do Something When'. Install it, then go into the System Preferences, choose 'DSW' and set up the rules similar to this:
Do Something When Setup
Change the 'When' to whatever you named your two TM drives (you will need to make a DSW rule for each TM drive you have), then change 'What>Open...' and navigate to the Application that you saved with Script Editor. Note that although you have two TM drives and two DSW rules, you still use ONE application/script to change the TM setting (e.g. you don't need two copies of the Application for this to work).
That's it. Now, when you hook up either of your drives, don't use the mouse for a few seconds, as the above script uses the GUI and any clicks you do on the mouse will invalidate the actions of the script. From now on, when you attach the drives, the System Preferences will open automatically, the Time Machine section will open, and the script will change disks for you. It will then close the System Preferences, and even give you a Growl notification (if you have Growl installed). Keep in mind that your first backup to each TM drive will seem to take years...
If you have any questions, feel free to ask. I have been using this since Leopard's launch and have had zero problems with it