---
title: How to manage data storage in a Data Warehouse for ClickHouse® deployment
description: This page explains how to manage data storage in a Data Warehouse for ClickHouse® deployment using storage policies
tags: data storage policy strategy options object block
dates:
  validation: 2025-10-16
  posted: 2025-10-16
---

import Requirements from '@macros/iam/requirements.mdx'

<Requirements />

- A Scaleway account logged into the [console](https://console.scaleway.com)
- [Owner](/iam/concepts/#owner) status or [IAM permissions](/iam/concepts/#permission) allowing you to perform actions in the intended Organization

## Overview

Scaleway Data Warehouse for ClickHouse® uses ClickHouse®'s native storage policies to decide where table data lives: on Scaleway Block storage, and/or on Object Storage (Amazon S3). Policies are applied at table-level during table creation, using the settings presented below. You can choose between three policies for your deployment:

- `tiered` (default in Scaleway Data Warehouse for ClickHouse®)
- `s3_cache` (cache mode)
- `default` (local-only mode)

The table below provides an overview of each storage policy's behavior and use case.

| Storage&nbsp;policy | Behavior | When to use |
|------|---------|------------|
| `tiered` | Writes on Block Storage first, and parts are automatically moved to Object Storage when disk is 90% full. | General purpose setting for fast local writes and transparent spillover to Object Storage as the dataset grows. |
| `s3_cache` | Data is stored on Object Storage. A local Block Storage cache layer keeps frequently-read parts to accelerate repeated reads. | Large datasets that mostly live in Object Storage, with repeated reads on smaller subsets that benefit from local caching. |
| `default` | Data is stored on Block storage only. | Small datasets where lowest latency for reads/writes on local disk is desired and capacity fits the Block Storage volume. |

## Tiered storage policy

### Applying the tiered policy

**Tiered** is the deployment's default policy. Data is stored on the `hot` volume (Block Storage) until it reaches 90% of its capacity, then data is moved to the `cold` volume. This mechanism is controlled by `move_factor:0.1`.

[Connect to you deployment](/data-warehouse/how-to/connect-applications/), then run the SQL query below to apply the `tiered` storage policy.

<Tabs>
  <TabsTab label="Explicit">
  
  Storage policy is explicitly defined as `tiered`.

    ```sql
    CREATE TABLE tiered_table
    (
      id UInt64,
      ts DateTime,
      value Float32
    )
    ENGINE = MergeTree
    PARTITION BY toYYYYMM(ts)
    ORDER BY id
    SETTINGS storage_policy = 'tiered';
    ```

  </TabsTab>
  <TabsTab label="Implicit">

    Storage policy is not defined, ClickHouse® applies the `tiered` storage policy by default.

    ```sql
    CREATE TABLE dw.tiered_table_implicit
    (
      id UInt64,
      ts DateTime,
      value Float32
    )
    ENGINE = MergeTree
    PARTITION BY toYYYYMM(ts)
    ORDER BY id;
    ```
  </TabsTab>
</Tabs>

<Message type="note">
If you omit the `storage_policy` setting, ClickHouse® will automatically apply the `tiered` policy.
</Message>

### Moving data with the tiered policy

When using the `tiered` storage policy, you can manually move partitions between `hot` (Block Storage) and `cold` (Object Storage) volumes using the SQL queries below.

- Moving specific partitions to the `cold` volume (Object Storage):

    ```sql
    ALTER TABLE tiered_table MOVE PARTITION '2024-08' TO VOLUME 'cold';
    ```

- Moving a non-partitioned table (`tuple()`) to the `cold` volume (Object Storage):

    ```sql
    ALTER TABLE tiered_table_without_partitions MOVE PARTITION tuple() TO VOLUME 'cold';
    ```

- Moving a partition to the `hot` volume (Block Storage):

    ```sql
    ALTER TABLE tiered_table MOVE PARTITION '2024-08' TO VOLUME 'hot';
    ```
- Moving a non-partitioned table (`tuple()`) to the `hot` volume (Block Storage):

    ```sql
    ALTER TABLE tiered_table_without_partitions MOVE PARTITION tuple() TO VOLUME 'hot';
    ```

## S3 cache policy

[Connect to your deployment](/data-warehouse/how-to/connect-applications/), then run the SQL query below to create a new table with the `s3_cache` policy enabled.
```sql
CREATE TABLE cache_table
(
  id UInt64,
  ts DateTime,
  value Float32
)
ENGINE = MergeTree
PARTITION BY toYYYYMM(ts)
ORDER BY id
SETTINGS storage_policy = 's3_cache';
```

## Local-only policy

[Connect to your deployment](/data-warehouse/how-to/connect-applications/), then run the SQL query below to create a new table with the `default` (Block Storage only) policy enabled.

```sql
CREATE TABLE local_table
(
  id UInt64,
  ts DateTime,
  value Float32
)
ENGINE = MergeTree
PARTITION BY toYYYYMM(ts)
ORDER BY id
SETTINGS storage_policy = 'default';
```