Here is a full description of backup for CRM on-prem:
http://msdn.microsoft.com/en-us/library/hh699676.aspx
The short is if you back up your organization CRM database, you can restore from just that if you needed.
Here is how you can get a backup copy of a CRM Online database:
http://msdn.microsoft.com/en-us/library/hh127043.aspx
The short there is Microsoft already is doing backups of CRM Online for DR, and you only really need a copy if you need to restore locally.
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