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Storage in {{ mmg-name }}

{{ mmg-name }} allows you to use network and local storage drives for database clusters. Network storage drives are based on network blocks, which are virtual disks in the {{ yandex-cloud }} infrastructure. Local disks are physically located in the database host servers.

{% include storage-type %}

Selecting disk type during cluster creation {#storage-type-selection}

The number of hosts you can create together with a {{ MG }} cluster depends on the selected disk type:

  • With local SSD (local-ssd) or non-replicated SSD (network-ssd-nonreplicated) storage, you can create a cluster with three or more hosts.

    This cluster will be fault-tolerant.

    Local SSD storage impacts the cost of a cluster: you are charged for it even if it is not running. For more information, refer to the pricing policy.

  • With network HDD (network-hdd) or network SSD (network-ssd) storage, you can add any number of hosts within the current quota.

For more information about limits on the number of hosts per cluster or shard, see Quotas and limits.

Managing disk space {#manage-storage-space}

{% include mmg-readonly-safeguard.md %}

After switching to read-only mode:

  • Write queries stop being allowed on the host. You can only make read queries.
  • If the host was a primary replica before switching to read-only mode, this role will be automatically assigned to another cluster host, as the primary replica role requires permission to write to the disk.

If the amount of data in the cluster keeps growing, all hosts will switch to read-only mode, one by one, and the cluster will stop accepting data to write.

Maintaining the health of a cluster {#read-only-solutions}

To make sure your cluster is healthy when the host switches to read-only mode:

  • Increase the disk space on the host. Once there is enough space on the host, {{ yandex-cloud }} will disable read-only mode automatically.

  • Add more shards to the cluster. Read-only mode will persist on this host, but the cluster will be able to continue working normally if there is free disk space on the other shards.

  • Contact [technical support]({{ link-console-support }}) and ask them to temporarily disable this host's read-only mode to manually delete a part of the data.

    {% note alert %}

    If you run out of free disk space completely, {{ MG }} will crash and the cluster will be disabled.

    {% endnote %}

  • Force data synchronization between hosts. This can help when a large amount of data was deleted from the cluster, but the disk space was not released (marked as available for reuse).