title: Cassandra Digest Mismatch Error
body: <p>I see the following message in Cassandra's debug.log frequently and sometimes before losing nodes in the cluster. Any ideas on what the message means, and how to fix the underlying issue?</p>
  
  <pre><code>    DEBUG [ReadRepairStage:9346] 2017-11-06 22:29:46,135  ReadCallback.java:242 - Digest mismatch:
  org.apache.cassandra.service.DigestMismatchException: Mismatch for key DecoratedKey(-8713145541289520569, 00114c65616465722f6d61737465722f352e3100000364633100) (408c7e13eea38efc9429366038cbe4a3 vs 8ce8acece0966903ac590d3229099398)
      at org.apache.cassandra.service.DigestResolver.compareResponses(DigestResolver.java:92) ~[cassandra-all-3.11.0.1900.jar:3.11.0.1900]
      at org.apache.cassandra.service.ReadCallback$AsyncRepairRunner.run(ReadCallback.java:233) ~[cassandra-all-3.11.0.1900.jar:3.11.0.1900]
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_151]
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_151]
      at org.apache.cassandra.concurrent.NamedThreadFactory.lambda$threadLocalDeallocator$0(NamedThreadFactory.java:81) [cassandra-all-3.11.0.1900.jar:3.11.0.1900]
      at java.lang.Thread.run(Thread.java:748) ~[na:1.8.0_151]
  </code></pre>
  
  <p>Here are the details of the Cassandra cluster:</p>
  
  <ul>
  <li>4 node cluster </li>
  <li>Each is an AWS instance of type m4.2xlarge </li>
  <li>Each has an io1 volume with 20000 IOPS </li>
  <li>All on same VPC, with 10.0.0.x private IP addresses </li>
  <li>DataStax Enterprise Server 5.1.5</li>
  </ul>