Enable DiskThresholdDecider by default, change default limits to 85/90%

Fixes #6200
Fixes #6201

docs/reference/index-modules/allocation.asciidoc

@@ -43,8 +43,8 @@ to be allocated to a node. This is in contrast to `include` which will
 include a node if ANY rule matches.
 
 The `include`, `exclude` and `require` values can have generic simple
-matching wildcards, for example, `value1*`. Additonally, special attribute 
-names called `_ip`, `_name`, `_id` and `_host` can be used to match by node 
+matching wildcards, for example, `value1*`. Additonally, special attribute
+names called `_ip`, `_name`, `_id` and `_host` can be used to match by node
 ip address, name, id or host name, respectively.
 
 Obviously a node can have several attributes associated with it, and
@@ -100,16 +100,18 @@ settings API.
 [[disk]]
 === Disk-based Shard Allocation
 
+coming[1.3.0] disk based shard allocation is enabled from version 1.3.0 onward
+
 Elasticsearch can be configured to prevent shard
 allocation on nodes depending on disk usage for the node. This
-functionality is disabled by default, and can be changed either in the
+functionality is enabled by default, and can be changed either in the
 configuration file, or dynamically using:
 
 [source,js]
 --------------------------------------------------
 curl -XPUT localhost:9200/_cluster/settings -d '{
     "transient" : {
-        "cluster.routing.allocation.disk.threshold_enabled" : true
+        "cluster.routing.allocation.disk.threshold_enabled" : false
     }
 }'
 --------------------------------------------------
@@ -118,15 +120,15 @@ Once enabled, Elasticsearch uses two watermarks to decide whether
 shards should be allocated or can remain on the node.
 
 `cluster.routing.allocation.disk.watermark.low` controls the low
-watermark for disk usage. It defaults to 70%, meaning ES will not
-allocate new shards to nodes once they have more than 70% disk
+watermark for disk usage. It defaults to 85%, meaning ES will not
+allocate new shards to nodes once they have more than 85% disk
 used. It can also be set to an absolute byte value (like 500mb) to
 prevent ES from allocating shards if less than the configured amount
 of space is available.
 
 `cluster.routing.allocation.disk.watermark.high` controls the high
-watermark. It defaults to 85%, meaning ES will attempt to relocate
-shards to another node if the node disk usage rises above 85%. It can
+watermark. It defaults to 90%, meaning ES will attempt to relocate
+shards to another node if the node disk usage rises above 90%. It can
 also be set to an absolute byte value (similar to the low watermark)
 to relocate shards once less than the configured amount of space is
 available on the node.

src/main/java/org/elasticsearch/cluster/routing/allocation/decider/DiskThresholdDecider.java

@@ -110,8 +110,8 @@ public class DiskThresholdDecider extends AllocationDecider {
     @Inject
     public DiskThresholdDecider(Settings settings, NodeSettingsService nodeSettingsService) {
         super(settings);
-        String lowWatermark = settings.get(CLUSTER_ROUTING_ALLOCATION_LOW_DISK_WATERMARK, "70%");
-        String highWatermark = settings.get(CLUSTER_ROUTING_ALLOCATION_HIGH_DISK_WATERMARK, "85%");
+        String lowWatermark = settings.get(CLUSTER_ROUTING_ALLOCATION_LOW_DISK_WATERMARK, "85%");
+        String highWatermark = settings.get(CLUSTER_ROUTING_ALLOCATION_HIGH_DISK_WATERMARK, "90%");
 
         if (!validWatermarkSetting(lowWatermark)) {
             throw new ElasticsearchParseException("Unable to parse low watermark: [" + lowWatermark + "]");
@@ -126,7 +126,7 @@ public class DiskThresholdDecider extends AllocationDecider {
         this.freeBytesThresholdLow = thresholdBytesFromWatermark(lowWatermark);
         this.freeBytesThresholdHigh = thresholdBytesFromWatermark(highWatermark);
 
-        this.enabled = settings.getAsBoolean(CLUSTER_ROUTING_ALLOCATION_DISK_THRESHOLD_ENABLED, false);
+        this.enabled = settings.getAsBoolean(CLUSTER_ROUTING_ALLOCATION_DISK_THRESHOLD_ENABLED, true);
         nodeSettingsService.addListener(new ApplySettings());
     }