Booting from an external disk
Solution 1:
You can use Option/Alt Key:
Shutdown your Mac
Make sure you have your external disk connected
Press Power Button to turn on your Mac
Before Apple Logo appears press Option/Alt Key and hold it
It should show all connected bootable disks
Select your external with arrows and press Enter
If your disks does not appear make sure that it is formatted with a GUID partition type.
For more info check this Link
I hope it helps you
Solution 2:
I understand that I can boot OS X from an external disk, but is that just as a means of recovery?
No, it can be for regular day use.
Can I actually setup and use OS X from an external disk to do work and save documents etc?
Yes, you can setup the Mac to always boot on an external drive (using System Preferences -> Startup disk). As well as use Allans reply above.
Solution 3:
You can totally boot from you external drive! This is what I did a week before I upgraded my iMac, I had it as an external then I put it in as an internal and continued where I left off. Was really smooth!
How to:
- Shutdown your Mac
- Connect external disk
- Turn on your Mac
- Press and hold Cmnd+R (for recovery)
- Choose Disk Utility
- Format your external drive as OS X Extended (Journaled) with "GUID Partition Map" scheme.
- Click on your newly formatted drive. Go up to Edit and click Restore.
- Select the drive you would like to clone. (The one with OSX installed, eg. Macintosh HD)
- After Restore, restart your Mac.
- Press and hold the Option key, then select the external drive to boot from it.
So you basically cloned your OS X onto an external drive and can work from it on any Mac you want, just hold Option key and boot from it anywhere. No need to use 3rd party software! :)
A video to help: https://www.youtube.com/watch?v=ivGKx2ec9UE