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.

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. To provision the IOPS rate of 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.


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.

Minimum Disk Capacity to RAM Ratios

Atlas enforces the following minimum ratios by cluster tier to facilitate consistent network performance with large datasets.

Disk Capacity to RAM:

  • < M40: 3:1
  • M40: 50:1
  • => M50: 100 to 1


A cluster with 50 GB storage requires a value for IOPS of at least 150. To support 3 TB of disk capacity, you must select a cluster tier with at least 32 GB of RAM (M50 or higher).

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 clusters with Auto-Expand Storage enabled, Atlas respects the calculated maximum storage for the selected cluster tier. Users whose disk capacity reaches the allowable limit receive notification by email.

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


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

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.

For more information on cluster auto-scaling and when auto-scaling occurs, see How Auto-Scaling Works.