What should I backup before installing a new ROM?

Question

What do I need to backup (using Titanium Backup) if I want to have the 'same system' after applying new version of a ROM?

Is it better to set up everything from scratch or restore my data from the backup?

I have a HTC Desire and I'm upgrading from CM rc2 to CM rc4

Answer 1

Jumping between ROMs in the same development series is usually safe without backing up or wiping the data partition (although the cache and Dalvik cache should always be wiped), unless the installation instructions specifically tell you to wipe the data partition (which seems unlikely in this case; if such a drastic change were needed, it shouldn't be a release candidate any more). I would nevertheless back everything up just in case, both application backup like Titanium Backup and Nandroid backup from the recovery partition, but then I'm paranoid like that.

Jumping to a different series (say, CM6 to CM7, or CM to aosp) you should always back up everything and wipe everything.

Answer 2

In order to avoid any possibility of data loss if something goes really wrong (never happened to me, but...) you should backup:

1. Installed applications, if you don't want to install all of the installed applications in case of failure.
2. Sent and received SMS, MMS
3. Photos and Videos if you stored it in the main memory (not common)
4. Contacts (only if not synchronized with a Gmail account).
5. Emails (only if not synchronized with a Gmail account).
6. Calendar (only if not synchronized with a Gmail account).

Basically if you want to be sure that nothing can go wrong, you need to backup all your data and configuration.

There are apps to do this, like Titanium backup