ClickHouse/docs/en/operations/system-tables/storage_policies.md

slug
/en/operations/system-tables/storage_policies

storage_policies

Contains information about storage policies and volumes defined in the server configuration.

Columns:

• policy_name (String) — Name of the storage policy.
• volume_name (String) — Volume name defined in the storage policy.
• volume_priority (UInt64) — Volume order number in the configuration, the data fills the volumes according this priority, i.e. data during inserts and merges is written to volumes with a lower priority (taking into account other rules: TTL, max_data_part_size, move_factor).
• disks (Array(String)) — Disk names, defined in the storage policy.
• volume_type (Enum8) — Type of volume. Can have one of the following values:
  • JBOD
  • SINGLE_DISK
  • UNKNOWN
• max_data_part_size (UInt64) — Maximum size of a data part that can be stored on volume disks (0 — no limit).
• move_factor (Float64) — Ratio of free disk space. When the ratio exceeds the value of configuration parameter, ClickHouse start to move data to the next volume in order.
• prefer_not_to_merge (UInt8) — Value of the prefer_not_to_merge setting. When this setting is enabled, merging data on this volume is not allowed. This allows controlling how ClickHouse works with slow disks.
• perform_ttl_move_on_insert (UInt8) — Value of the perform_ttl_move_on_insert setting. — Disables TTL move on data part INSERT. By default if we insert a data part that already expired by the TTL move rule it immediately goes to a volume/disk declared in move rule. This can significantly slowdown insert in case if destination volume/disk is slow (e.g. S3).
• load_balancing (Enum8) — Policy for disk balancing. Can have one of the following values:
  • ROUND_ROBIN
  • LEAST_USED

If the storage policy contains more then one volume, then information for each volume is stored in the individual row of the table.