Low disk space watermarks
OpenSearch® relies on three indicators to identify and respond to low disk space.
Disk allocation low watermark
Defined by parameter cluster.routing.allocation.disk.watermark.low
and
the default value is set to 85% of the disk space.
When this limit is exceeded, OpenSearch starts avoiding allocating new shards to the server. On a single-server OpenSearch, this has no effect. On a multi-server cluster, amount of data is not always equally distributed, in which case this will help balancing disk usage between servers.
Disk allocation high watermark
Defined by parameter cluster.routing.allocation.disk.watermark.high
and the default value is set to 90% of the disk space.
When this limit is exceeded, OpenSearch will actively try to move shards to other servers with more available disk space. On a single-server OpenSearch, this has no effect.
Disk allocation flood stage watermark
Defined by parameter
cluster.routing.allocation.disk.watermark.flood_stage
and the default
value is set to 95% of the disk space.
When this limit is exceeded, OpenSearch will mark all indices hosted on
the server exceeding this limit as read-only, allowing deletes
(index.blocks.read_only_allow_delete
).