Cloudera Docs

HDFS storage policies

A storage policy contains information that describes the type of storage to use. This policy also defines the fallback storage type if the primary type is out of space or out of quota. If a target storage type is not available, HDFS attempts to place replicas on the default storage type.

Each storage policy consists of a policy ID, a policy name, a list of storage types, a list of fallback storage types for file creation, and a list of fallback storage types for replication.

HDFS has six preconfigured storage policies.
  • Hot - All replicas are stored on DISK.
  • Cold - All replicas are stored ARCHIVE.
  • Warm - One replica is stored on DISK and the others are stored on ARCHIVE.
  • All_SSD - All replicas are stored on SSD.
  • One_SSD - One replica is stored on SSD and the others are stored on DISK.
  • Lazy_Persist - The replica is written to RAM_DISK and then lazily persisted to DISK.