Unassigned primary shards

Question

Using ES 1.5.2

When a primary shard is unassigned. Does it mean the data is lost?

I had some unassigned primaries tried to re-allocate them with the allocate command, but the index didn't go back to it's original size.

Answer 1

There shouldn't be any data loss, one of the the master node's roles is specifically to retrieve all the data in the soon-to-be unassigned shard and dispatch it across all the other available shards.