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The "Operations" page has been changed by PeterSchuller.
The comment on this change is: Warn about not running repair at the same time 
on all nodes.
http://wiki.apache.org/cassandra/Operations?action=diff&rev1=76&rev2=77

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  === Frequency of nodetool repair ===
  
  Unless your application performs no deletes, it is vital that production 
clusters run `nodetool repair` periodically on all nodes in the cluster. The 
hard requirement for repair frequency is the value used for GCGraceSeconds (see 
[[DistributedDeletes]]). Running nodetool repair often enough to guarantee that 
all nodes have performed a repair in a given period GCGraceSeconds long, 
ensures that deletes are not "forgotten" in the cluster.
+ 
+ Consider how to schedule your repairs. A repair causes additional disk and 
CPU activity on the nodes participating in the repair, and it will typically be 
a good idea to spread repairs out over time so as to minimize the chances of 
repairs running concurrently on many nodes.
  
  ==== Dealing with the consequences of nodetool repair not running within 
GCGraceSeconds ====
  

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