title: Cassandra Write ahead log and memtables flush to disk
body: <p>Been reading up on a Cassandra, and I get the feeling thats its REALLY not fault tolerant, is it?</p>
  
  <p>I mean, take a very simple scenario, incoming write, you write to to the WAL, to the memtable and then mark in the WAL that the write succeeded and then the server crashes before the memtable gets full so its not flushed to disk as an SSTable, meaning I just lost this write + I wont be able to redo it since its marked as "Done" in the WAL.</p>
  
  <p>Am I missing something here or is it really not fault tolerant? Which seems very weird to me since its used in so many places and for so much data, which makes me think im missing something.</p>