What to back up?

Question

I want to jump from tiger to snow leopard. I wanted to just do the upgrade option on top of tiger but people have been saying that I should erase and do a clean install.
I'm in the process of creating some backups now with SuperDuper.
Do I need to backup everything? I only want some of my applications, all of my photos+music etc are all on external drives already.
Do I need to backup /system, /private, /library? Can I just backup /Users?
When I do create the backup, do I create a disk image? Or just transfer to another drive?
How will this work with migration assistant?

Answer 1

I want to jump from tiger to snow leopard. I wanted to just do the upgrade option on top of tiger but people have been saying that I should erase and do a clean install.
That may not be necessary, but the backup issues you mention should be addressed regardless. See my [Mac Backup Guide|http://www.reedcorner.net/thomas/guides/backups> for more info.
Do I need to backup everything?
When doing a major upgrade like this, it is generally a good idea to have a complete backup of everything on your boot drive. That way, if there are incompatibilities with old hardware/software, if something goes wrong and the system gets damaged, etc, you have a quick and easy way to restore to the previous state.
I only want some of my applications
Note that you should have copies of installers for all apps that require one. If you are going to go to the trouble of doing a clean install, you should reinstall apps from scratch. If you copy apps over from the old system, it's no longer a completely clean install.
all of my photos+music etc are all on external drives already.
Do you have a backup of all those things? Not that it's particularly relevant to a system upgrade, but you should not fool yourself into thinking that just because they're on an external drive, they're safe. If that drive fails, you need to be prepared or you'll loose all that stuff.
When I do create the backup, do I create a disk image? Or just transfer to another drive?
I would avoid disk images. One teeny bit of corruption and the whole thing becomes unusable. If you're using SuperDuper, just have it copy the files to the backup drive.
How will this work with migration assistant?
If you use something like SuperDuper to create a "clone" of your boot drive (meaning an exact copy on another drive), then I would think Migration Assistant could help import data from there into the new system. After all, there's no difference between that and your boot disk, except for physical location. OTOH, if you tell it to copy everything into a folder on an external drive, it wouldn't look the same as a boot drive and MA might fail. Just be cautious with what you import using MA... again, if you do a clean install and then import all your apps and settings from the old system, you've wasted the time it took to do the clean install. You might as well have just installed over the old system.