elasticsearch/docs/reference/upgrade/disable-shard-alloc.asciidoc

When you shut down a data 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
<<cluster-routing-allocation-enable,disabling allocation>> of replicas before
shutting down <<data-node,data nodes>>:

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