[Yandex Cloud documentation](../../index.md) > [Yandex Managed Service for MySQL®](../index.md) > FAQ > Updating a cluster

# Updating a MySQL® cluster


* [Can I manage a cluster using SQL commands?](#sql-control)

* [How do I reduce the size of a disk?](#reduce-size)

* [How do I increase the size of a disk?](#increase-size)


* [How do I change the disk type?](#modify-type)

* [Why cannot I add or delete a host?](#not-add-delete)

* [How do I perform a manual failover?](#manual-failover)

* [How do I restart a host?](#host-reboot)

* [Why do I get an error when stopping the cluster?](#stop-cluster-error)

#### Can I manage a cluster using SQL commands? {#sql-control}

Cluster management via SQL commands has certain restrictions. For more information, see [SQL command limits](../concepts/sql-limits.md).

#### How do I reduce the size of a disk? {#reduce-size}

You cannot reduce the size of a cluster storage.

You can [create](../operations/cluster-create.md) a new cluster with smaller storage and [migrate](../tutorials/data-migration/index.md) your data to it.

#### How do I increase the size of a disk? {#increase-size}

You cannot directly increase the size of non-replicated SSD [storage](../concepts/storage.md): follow the steps outlined in [this guide](../operations/update.md#change-disk-size).

If you need it increased, [restore the cluster from a backup](../operations/cluster-backups.md#restore) and set the appropriate size.

You can check the disk type in the [management console](https://console.yandex.cloud). To do this, find the **Storage** setting under **Resources** on the cluster page.


#### How do I change the disk type? {#modify-type}

To change the disk type, [restore](../operations/cluster-backups.md#restore) your cluster from a backup.

#### Why cannot I add or delete a host? {#not-add-delete}

The number of hosts in clusters is limited by [quotas](../concepts/limits.md#mmy-quotas). Before adding a host, check the resources currently in use: open the [Quotas](https://console.yandex.cloud/cloud?section=quotas) page and find the **Managed Databases** section.

You can delete a host as long as it is not the only host in the cluster. To replace the only host, first create a new host and then delete the old one.

Clusters with local disks have a fault-tolerant three-host configuration. Using fewer hosts is not allowed.

#### How do I perform a manual failover? {#manual-failover}

In a fault-tolerant multi-host cluster, you can switch the master role from the current master host to a replica host. After the failover, the current master host becomes a replica for the new master.

{% list tabs group=instructions %}

- Management console {#console}

   1. Go to the cluster page and select the **Hosts** tab.
   1. Click **Switch master**.

- CLI {#cli}

   If you do not have the Yandex Cloud CLI yet, [install and initialize it](../../cli/quickstart.md#install).

   The folder used by default is the one specified when [creating](../../cli/operations/profile/profile-create.md) the CLI profile. To change the default folder, use the `yc config set folder-id <folder_ID>` command. You can also specify a different folder for any command using `--folder-name` or `--folder-id`. If you access a resource by its name, the search will be limited to the default folder. If you access a resource by its ID, the search will be global, i.e., through all folders based on access permissions.

   To switch the master:

   1. See the description of the CLI command for initiating a failover:

      ```bash
      yc managed-mysql cluster start-failover --help
      ```

   1. Run the `yc managed-mysql cluster start-failover` command.

{% endlist %}

#### How do I restart a host? {#host-reboot}

You cannot restart a separate cluster host. To restart hosts, [stop and restart the cluster](../operations/cluster-stop.md).

#### Why do I get an error when stopping the cluster? {#stop-cluster-error}

Error message:

```text
cluster has no backups. If you want to stop the cluster, make a backup
```

The error occurs because you can stop an Managed Service for MySQL® cluster only if there is at least one backup of the cluster.

**Solution**: Wait until an automatic backup is created or [create a backup manually](../operations/cluster-backups.md#create-backup).