system.disk_types

System table containing a list of disk types supported by the server along with their embedded documentation.

Description

Contains the list of disk types supported by the server, along with embedded documentation for each type. A disk type is specified in the type of a disk configuration and determines where and how a disk stores its data (local filesystem, object storage, a cache over another disk, and so on).

Note that this table lists the available disk types, whereas system.disks lists the disk instances configured on the server.

Columns

• name (String) — The name of the disk type, as specified in the type of a disk configuration.
• description (String) — A high-level description of what the disk type does.
• syntax (String) — How the disk type is specified in a disk configuration.
• examples (String) — Usage examples.
• introduced_in (String) — The ClickHouse version in which the disk type was first introduced, in the form major.minor.
• related (Array(String)) — The names of related disk types.

Configuration examples

A disk can be configured in two ways: statically, in the server configuration files (XML or YAML), or dynamically, in the settings of a CREATE/ATTACH query using the disk function. The same disk type and parameters are accepted in both cases.

Static configuration

Disks are defined under storage_configuration in the server configuration. The following example defines an s3 disk and a storage policy that uses it.

config.xml

<clickhouse>
    <storage_configuration>
        <disks>
            <s3_disk>
                <type>s3</type>
                <endpoint>https://s3.eu-west-1.amazonaws.com/clickhouse-eu-west-1.clickhouse.com/data/</endpoint>
                <use_environment_credentials>1</use_environment_credentials>
            </s3_disk>
        </disks>
        <policies>
            <s3_policy>
                <volumes>
                    <main>
                        <disk>s3_disk</disk>
                    </main>
                </volumes>
            </s3_policy>
        </policies>
    </storage_configuration>
</clickhouse>

The same configuration in YAML:

config.yaml

storage_configuration:
  disks:
    s3_disk:
      type: s3
      endpoint: https://s3.eu-west-1.amazonaws.com/clickhouse-eu-west-1.clickhouse.com/data/
      use_environment_credentials: 1
  policies:
    s3_policy:
      volumes:
        main:
          disk: s3_disk

A table can then use the disk through its storage policy:

Query

CREATE TABLE test (a Int32, b String)
ENGINE = MergeTree() ORDER BY a
SETTINGS storage_policy = 's3_policy';

Dynamic configuration

A disk can also be defined directly in the settings of a CREATE/ATTACH query, without a predefined disk in the configuration files, using the disk function:

Query

CREATE TABLE test (a Int32, b String)
ENGINE = MergeTree() ORDER BY a
SETTINGS disk = disk(
    type = s3,
    endpoint = 'https://s3.eu-west-1.amazonaws.com/clickhouse-eu-west-1.clickhouse.com/data/',
    use_environment_credentials = 1
);

See Configuring external storage for the full list of parameters of each disk type.

Example

Query

SELECT name, description
FROM system.disk_types
WHERE name IN ('local', 'object_storage')
ORDER BY name

See also

• system.disks — The disk instances configured on the server.
• system.storage_policies — Storage policies and volumes.