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what is our Recovery Time Objective? (how soon to be back up and running)
http://en.wikipedia.org/wiki/Recovery_Time_Objective
access to the database is more important than access to the cached map data
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If no replication, how much work can we loose? (1 day, 4 hours?, 2 hours?)
Recovery Point Objective (acceptable amount of data loss measured in time)
http://en.wikipedia.org/wiki/Recovery_point_objective