at the time they picked HBase because it was easier to repair missing replicas. Hdfs namenode juat schedules block replication. Cassandra (at least the version they were considering) had to work a lot harder at replacing a missing replica. Remember they had a version that didn’t have workable merkel trees.

I also heard they had an issue with network flaps causing unrepairable inconsistency. I never got the full scoop on this.

I had worked with the engineers directly responsible for the HBase choice back when. All water under the bridge now it seems.