When you shut down a node, the allocation process waits for
`index.unassigned.node_left.delayed_timeout` (by default, one minute) before
starting to replicate the shards on that node to other nodes in the cluster,
which can involve a lot of I/O.  Since the node is shortly going to be
restarted, this I/O is unnecessary. You can avoid racing the clock by 
<<shards-allocation, disabling allocation>> of replicas before shutting down
the node:

[source,js]
--------------------------------------------------
PUT _cluster/settings
{
  "persistent": {
    "cluster.routing.allocation.enable": "primaries"
  }
}
--------------------------------------------------
// CONSOLE
// TEST[skip:indexes don't assign]