@sim6 I hope you have more than 3 data nodes Generally there two types of "data missing" issues are possible for many reasons a. ReplicaNotFoundException b. BlockMissingException If your issue is related to BlockMissingException and if you have backup data in your DR environment then you are good otherwise it might be a problem, but for ReplicaNotFoundException, please make sure all your datanodes are healthy and commissioned state. In fact, namenode suppose to handle this automatically whenever a hit occurs on that data.. if not, you can also try hdfs rebalance (or) NN restart may fix this issue, but you don't need to try this option unless some user report any issue on the particular data. In your case no one reported yet and you found it, so you can ignore it for now
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