Hard to answer, not because technical difficulty - but psychology. ;) So I will take take the answer a bit easy...
A. The simple way
Make an TimeMachine backup. (if you do 1st times will get a full backup) so you will able restore anything what you created on the Mac. For this you will need:
- one external HDD (big enough), connect it
- go to system prefs
- use this extrnal HDD as Backup disk for the TimeMachine
B. As A. but with an boot-able time machine HDD
For this you will need:
- one external HDD (big enough)
- your OS X install DVD
- turn off time machine, if you have it on
- connect HDD
- insert install DVD
- start /Applications/Utilities/DiskUtility.app
- select your external HDD
- go to "Restore" Tab
- into "Source field" drag your Install DVD
- into "Deststination" drag your external HDD
- triple check (so DON'T ERASE YOUR INTERNAL HDD!)
- press Restore and going to take a lunch
- after the restore, exit Disk Utility
- eject Install DVD
- go to System Prefs and enable Time machine
- select your external HDD as BackupDrive
- Make a full Time Machine backup
With the above you get a BOOTABLE TimeMachine HDD, you when things going wrong you can hold down Alt whe you MAc booting a can select this HDD for BOOT and restore from it without needing the install dvd (faster restore).
C. Want even more?
Make working copy of your HDD. It is like above, will got an BOOTABLE external HDD, but not for install purpose, but for working from it. So, you can boot it and continue work as from your internal HDD.
For this you can:
- get a donation-ware: CarbonCopyCloner, or
- make a normal install into external HDD, boot it, and use the MigrationAssistant.app to migrate data from the internal HDD to freshly installed external HDD
Do you know than paranoia is the right state of the system administrator's mind?
Do B and C - So you will need two external HDD's. Is is the best, because you can drop your backup HDD from table, and after this crash-test the drive will be probably unusable (broken). :) Anyway, for this solution you need do not crash-test both drives.
With this, you will can WORK immediately (from the external drive) and restore from the TimeMachine (from the second ext.HDD).
- Anything that can go wrong, will go wrong. (Hang up Murphy!)
- Your upgrade will fail (but usually it doesn't)
- Your backup will fail too (but usually you don't need it)
- so... take it easy ;)
Here is more ways, e.g.: over the network from the command line with
rsync command, etc. etc...
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