Navigation

Customize Cluster Storage

Each cluster tier comes with a default set of resources. Clusters of size M10 and larger provide the ability to customize your storage capacity.

Image showing storage customization

Atlas provides the following storage configuration options, depending on the selected cloud provider and cluster tier.

Cluster Class (AWS only)

Clusters of size M40 and larger on AWS offer multiple options, including:

  • Low CPU
  • General
  • Local NVMe SSD

Locally attached ephemeral NVMe SSDs offer the highest level of speed and performance.

Select the Class box with your preferred speed. Changes to cluster class affect cost.

Storage Capacity

The size of the server data volume. To change this, either:

  • Specify the exact disk size in the text box, or
  • Move the slide bar until the text box displays your preferred disk size.

Changes to storage capacity affect cost.

Note

When you increase the storage capacity of a cluster, Atlas increases the cluster’s oplog size. Atlas scales the oplog to 5% of the cluster capacity, not to exceed 50 GB. NVMe storage requires an oplog which is 10% of the storage capacity. Atlas doesn’t change the oplog size if it exceeds 5% of the new storage capacity (10% in the case of NVMe storage).

As cluster storage capacity decreases, Atlas doesn’t change the oplog size unless it exceeds a certain maximum determined according to MongoDB best practices.

Changing Storage Capacity on AWS

AWS allows one storage capacity upgrade every six hours. When you upgrade a cluster’s storage capacity for the first time during a six-hour period, Atlas modifies the size of the servers’ data volumes with zero downtime. If you upgrade the cluster’s storage capacity again within six hours, Atlas provisions new volumes and synchronizes data from the old to the new volumes to work around the AWS limitation. During this time, you can still access your cluster, but each node that AWS modifies is unavailable until AWS attaches the new volume.

AWS does not allow in-place storage capacity downgrades. If you downgrade a cluster’s storage capacity, Atlas provisions new volumes and synchronizes data from the old to the new volumes to work around the AWS limitation. During this time, you can still access your cluster, but each node that AWS modifies is unavailable until AWS attaches the new volume.

This behavior also applies when you enable storage auto-scaling and Atlas changes cluster storage.

To learn more about AWS volume modification limitations, see Requirements When Modifying Volumes in the AWS documentation.

IOPS (configurable for AWS only)

Atlas clusters on AWS of size M30 and greater allow you to customize the maximum IOPS rate of your cluster. Low-CPU or general class clusters of M30 or greater tiers have a minimum of ratio of IOPS to storage of 3:1. You can’t change the IOPS of a local NVMe SSD class cluster. To set a greater IOPS rate for your cluster, select Provision IOPS and either:

  • Specify the exact IOPS rate in the text box, or
  • Move the slide bar until the text box displays your preferred IOPS rate.

Note

The available IOPS range for a cluster relates to disk storage capacity. Changing your cluster’s storage capacity changes the range of available IOPS.

The default IOPS rate changes as the cluster’s storage capacity changes. If you want to provision an exact IOPS value, enable provisioning.

Changes to IOPS provisioning affect characteristics, performance and cost. When you select Provision IOPS, the storage changes from General Purpose SSD (gp2) volumes to Provisioned IOPS SSD (io1) volumes.

If you select or deselect Provision IOPS for an existing cluster, Atlas provisions new volumes and synchronizes data from the old to the new volumes.

Minimum Disk Capacity to RAM Ratios

Atlas enforces the following minimum ratios for given cluster tiers. This keeps network performance consistent with large datasets.

Tier Ratio of Disk Capacity : System Memory
M10 - M40 60:1
=> M50 120:1

Example

To support 3 TB (or 3,072 GB) of disk capacity, select a cluster tier with a minimum of 32 GB of RAM. This would be M50 or greater.

Atlas has a 4 TB disk capacity limit on all replica sets and shards, regardless of cluster tier. To expand total cluster storage beyond 4 TB, enable sharding.

For more information on the default resources and available configuration options for each cloud service provider, see:

Auto-Scale Cluster Tier and Storage Capacity

Feature Availability

Cluster Auto-Scaling is available for M10+ clusters using the General instance class.

Use Auto-scale options to configure your cluster to automatically scale your cluster tier, storage capacity, or both in response to cluster usage. Cluster storage auto-scaling is enabled by default.

Image showing the auto-scaling cluster options.

To configure your cluster to automatically scale its cluster tier, check the Cluster tier checkbox. When you enable cluster tier scaling, by default, your cluster can only scale up. To allow your cluster to scale down, check the Allow cluster to be scaled down checkbox. Specify a range of cluster tiers to which your cluster can scale.

To opt out of cluster storage scaling, un-check the Storage checkbox.

To learn more about cluster auto-scaling and when auto-scaling occurs, see Cluster Auto-Scaling.