I want to 'persist' my Amazon EC2 images. My scenario:

• I have a range of Windows and Linux machines
  
• Some machines are EBS backed, whereas others are S3 backed.
  
• I need to be able to persist a machine (put it to sleep), preferably keeping all settings active I had them when the machine was running.
  
• I need to be able to quickly wake up a machine from sleep [Ideally with an SLA of less than 2 min to turn-on, if such an SLA is available with Amazon].

Here's the stuff that confuses me:

• AWS allows me to put EBS backed machines to sleep, but not S3 backed.
  
• I believe I can put S3 machines into some sort of persistence mode. But this involves shutting down the machine, writing it to S3 storage and then recovering from there (not a real sleep mode, but at least I don't continue to get billed for CPU).
  
• S3 backing seems to take a long time to either writing a machine to disk, or to recover (turn on a machine).
  
• I can't tell immediately which machines are EBS backed and which are S3 backed? It seems like I can instantiate either type, but it's not immediately clear how Amazon decided whether a given machine should be EBS or S3 backed.
  

Advice?