title: Urgent:Do we need repair when we add new Data center in Cassandra
body: <p>We are adding a data center to existing dc. As we want to add new dc without downtime, we ran traffic on existing dc while we were performing the last step of rebuilding new nodes from existing dc. We observed that some read requests failed on first attempt but were successful on second attempt. Seem to an issue with data getting out of sync on existing cluster and then read repair fixing it.</p>
  
  <p>Question:Why did data on existing cluster got out of sync? Adding dc steps never tell you to do repair. Is it the Alter statement which added RF for DC2 (DC1:3 DC2:3) which resulted in out of sync data or rebuild procedure?</p>
  
  <p>I am using Cassandra 2.0.3</p>