First off let me in advance apologize for the probably dumb question but I am fairly new to Elasticsearch.
This all assumes that the master nodes are dedicated and running.
I am trying to do disaster recovery planning and I am not seeing (or not understanding completely how Elasticsearch works) how to calculate for data node failures. An example of this would be if I had 4 data nodes and each index has 5 shards and 1 replica how many data nodes can I lose at once? Lets say that 2 of the 4 nodes are in a single rack and the rack goes down. What if a single node fails and allows time to replicate and bring up all the replica shards then another node fails?
I was trying to find a formula or something that would say if you have X nodes with X shards and X replicas this is what will happen? Or is it the data is still available as long as one node is up and happens to have a single shard of that index?
Any info or help or links would be greatly appreciated.