[role="xpack"] [[data-tiers]] == Data tiers A _data tier_ is a collection of nodes with the same data role that typically share the same hardware profile: * <> nodes handle the indexing and query load for content such as a product catalog. * <> nodes handle the indexing load for time series data such as logs or metrics and hold your most recent, most-frequently-accessed data. * <> nodes hold time series data that is accessed less-frequently and rarely needs to be updated. * <> nodes hold time series data that is accessed infrequently and not normally updated. * <> nodes hold time series data that is accessed rarely and never updated, kept in searchable snapshots. When you index documents directly to a specific index, they remain on content tier nodes indefinitely. When you index documents to a data stream, they initially reside on hot tier nodes. You can configure <> ({ilm-init}) policies to automatically transition your time series data through the hot, warm, and cold tiers according to your performance, resiliency and data retention requirements. A node's <> is configured in `elasticsearch.yml`. For example, the highest-performance nodes in a cluster might be assigned to both the hot and content tiers: [source,yaml] -------------------------------------------------- node.roles: ["data_hot", "data_content"] -------------------------------------------------- [discrete] [[content-tier]] === Content tier Data stored in the content tier is generally a collection of items such as a product catalog or article archive. Unlike time series data, the value of the content remains relatively constant over time, so it doesn't make sense to move it to a tier with different performance characteristics as it ages. Content data typically has long data retention requirements, and you want to be able to retrieve items quickly regardless of how old they are. Content tier nodes are usually optimized for query performance--they prioritize processing power over IO throughput so they can process complex searches and aggregations and return results quickly. While they are also responsible for indexing, content data is generally not ingested at as high a rate as time series data such as logs and metrics. From a resiliency perspective the indices in this tier should be configured to use one or more replicas. The content tier is required. System indices and other indices that aren't part of a data stream are automatically allocated to the content tier. [discrete] [[hot-tier]] === Hot tier The hot tier is the {es} entry point for time series data and holds your most-recent, most-frequently-searched time series data. Nodes in the hot tier need to be fast for both reads and writes, which requires more hardware resources and faster storage (SSDs). For resiliency, indices in the hot tier should be configured to use one or more replicas. The hot tier is required. New indices that are part of a <> are automatically allocated to the hot tier. [discrete] [[warm-tier]] === Warm tier Time series data can move to the warm tier once it is being queried less frequently than the recently-indexed data in the hot tier. The warm tier typically holds data from recent weeks. Updates are still allowed, but likely infrequent. Nodes in the warm tier generally don't need to be as fast as those in the hot tier. For resiliency, indices in the warm tier should be configured to use one or more replicas. [discrete] [[cold-tier]] === Cold tier When data is no longer being updated, it can move from the warm tier to the cold tier where it stays while being queried infrequently. As data transitions into the cold tier, it can be compressed and shrunken. Instead of using replicas, the cold tier can use <> of <> for resiliency, eliminating the need for replicas. The cold tier is still a responsive query tier, but data becomes read-only. [discrete] [[frozen-tier]] === Frozen tier Once data is no longer being queried, or being queried rarely, it may move from the cold tier to the frozen tier where it stays for the rest of its life. The frozen tier uses <> to store and load data from a snapshot repository. This reduces local storage and operating costs while still letting you search frozen data. Because {es} must sometimes fetch frozen data from the snapshot repository, searches on the frozen tier are typically slower than on the cold tier. NOTE: We recommend you use <> in the frozen tier. [discrete] [[data-tier-allocation]] === Data tier index allocation When you create an index, by default {es} sets <> to `data_content` to automatically allocate the index shards to the content tier. When {es} creates an index as part of a <>, by default {es} sets <> to `data_hot` to automatically allocate the index shards to the hot tier. You can explicitly set `index.routing.allocation.include._tier_preference` to opt out of the default tier-based allocation. [discrete] [[data-tier-migration]] === Automatic data tier migration {ilm-init} automatically transitions managed indices through the available data tiers using the <> action. By default, this action is automatically injected in every phase. You can explicitly specify the migrate action with `"enabled": false` to disable automatic migration, for example, if you're using the <> to manually specify allocation rules.