Basically comes down to the CAP theorem:
You have to pick two of Consistency, Availability, and Partition tolerance. You can’t have all 3.
Cassandra chooses AP, though you can get consistency if you can tolerate greater latency.
By default provides weak consistency
Hbase values CP, but availability may suffer.
In the event of a partition (node failure), the data won’t be available if it can’t be guaranteed to be consistent with committed operation.