You are looking at preliminary documentation for a future release. Not what you want? See the current release documentation.
allocation provides a snapshot of how many shards are allocated to each data node
and how much disk space they are using.
Might respond with:
shards disk.indices disk.used disk.avail disk.total disk.percent host ip node 1 260b 47.3gb 43.4gb 100.7gb 46 127.0.0.1 127.0.0.1 CSUXak2
Here we can see that the single shard created has been allocated to the single node available.