Customize Cluster Storage

On this page

Cluster Class

Low CPU Class
NVMe Storage on AWS
Storage Capacity
Oplog Scaling Behavior
Change Storage Capacity or IOPS on AWS
Change Storage Capacity on Azure
Change Storage Capacity on Google Cloud
Change Storage Capacity for Multi-Cloud Provider Clusters
IOPS (AWS Only)
Provisioned IOPS vs Standard IOPS in AWS
Configure the IOPS Rate
Minimum Disk Capacity to RAM Ratios
Auto-Scale Cluster Tier and Storage Capacity

Each cluster tier comes with a default set of resources. M10+ clusters provide the ability to customize your storage capacity.

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

Cluster Class

M40+ clusters offer multiple options, including:

Low CPU
General
Local NVM SSD

All production environments can use the General option.

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

Low CPU Class

The Low CPU option offers a lower-cost alternative for applications that require more memory and fewer CPUs. This option includes half the vCPUs of an instance with the General option. For example, a General M40 instance includes 4 vCPUs, while a Low CPU M40 instance includes 2 vCPUs. Depending on the cluster tier, this option may also include fewer max connections. To learn more, see Connection Limits and Cluster Tier.

NVMe Storage on AWS

AWS-backed clusters have the added Local NVMe SSD storage option. Locally attached ephemeral NVMe SSDs offer the highest level of speed and performance.

Storage Capacity

To change the server data volume size, do one of the following tasks:

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

Changes to storage capacity affect cost.

Note

MongoDB uses a small portion of your specified storage capacity for buffer files, journal files, and log files to ensure proper cluster operation.

Oplog Scaling Behavior

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.

Change Storage Capacity or IOPS on AWS

Atlas handles changes differently based on whether you want to increase or decrease storage capacity or storage throughput (IOPS) on AWS.

Increase Capacity or Throughput

AWS allows you to increase storage capacity or IOPS every six hours. Atlas supports more changes within that six-hour window.

How Atlas handles additional changes within a six-hour window depends on the size of your hosts' data volumes and the time when you make the change in the six-hour window.

For the first change, Atlas modifies data volumes in place without downtime.

For later changes:

Data Volume Size	Time Since Last Storage Change	Action Atlas Takes
Less than 1TB	Less than 5h30m	Atlas provisions new volumes and syncs the data from the old volumes. If Atlas provisions new volumes, you can access your cluster. You can't access nodes that AWS modifies until AWS attaches the new volume.
Less than 1TB	More than 5h30m	Atlas waits until the six-hour window closes, then modifies the hosts' data volumes in place without downtime.
More than 1TB	Any	Atlas waits until the six-hour window closes, then modifies the hosts' data volumes in place without downtime. This takes less time than provisioning new volumes and syncing data from the old to the new volumes.

Before you apply your storage capacity or IOPS increases, the Review Changes page describes how Atlas approaches the increase.

The Database Deployments page displays a banner if Atlas waits until a six-hour window closes before modifying your cluster's storage capacity or IOPS.

These behaviors apply when Atlas changes capacity during auto-scaling.

To learn more about AWS's limitations, see the AWS documentation.

Decrease Capacity or Throughput

AWS doesn't allow you to reduce storage capacity in place.
Atlas can reduce storage capacity in place. Atlas provisions new volumes then syncs data from the old to the new volumes. This works around the AWS limitation.
AWS does allow you to reduce IOPS without migrating data.

Change Storage Capacity on Azure

When you change a cluster's storage capacity, Atlas modifies the size of the servers' data volumes in a rolling manner with zero downtime.

Atlas increases the storage capacity in place without copying data or performing an initial sync. However, Azure doesn't allow in-place storage capacity downgrades. If you downgrade the storage capacity of a cluster, Atlas replaces each node and performs an initial sync for each node in the cluster.

Note

An initial sync copies data across the network and rebuilds all indexes.

During this time, you can still access your cluster, but each node that Azure modifies remains unavailable until the initial sync for that node completes.

Important

For large clusters, initial syncs for each node might take several hours to complete.

Before you apply your storage capacity changes, the Review Changes page notifies you that Atlas triggers a rolling restart of your cluster when you make this change.

Change Storage Capacity on Google Cloud

When you change a cluster's storage capacity, Atlas modifies the size of the servers' data volumes in a rolling manner with zero downtime.

Atlas increases the storage capacity in place without copying data or performing an initial sync. However, Google Cloud doesn't allow in-place storage capacity downgrades.

If you downgrade the storage capacity of a cluster, Atlas provisions new volumes, and then syncs data from the old to the new volumes.

Before you apply your storage capacity changes, the Review Changes page notifies you that Atlas triggers a rolling restart of your cluster when you make this change.

Change Storage Capacity for Multi-Cloud Provider Clusters

Atlas selects the lowest common denominator across the three cloud providers. This ensures consistency across the multi-cloud deployment.

You can't adjust the IOPS for your multi-cloud cluster.

If your multi-cloud cluster includes Azure, storage capacity can be changed only in preset increments.

IOPS (AWS Only)

AWS-backed M30+ clusters offer the option to provision IOPS.

Provisioned IOPS vs Standard IOPS in AWS

Provisioned IOPS let you customize the maximum IOPS rate for your cluster. They also:

Deliver their configured IOPS rate more consistently when compared to standard IOPS.
Lower your cluster's p90 latency (measurement of the server's response time). 90 percent of server requests have responses faster than the p90 latency value, so a lower p90 latency value means a generally faster response time.

To learn more about the merits of using provisioned vs standard IOPS, see Amazon EBS-optimized instances. See the following summary:

General Purpose SSD volumes are designed to deliver their baseline performance 99% of the time.
Provisioned IOPS SSD volumes are designed to deliver their provisioned performance 99.9% of the time.

Note

Changes to IOPS provisioning affects characteristics, performance, and cost. When you select Provision IOPS, the storage changes from General Purpose SSD volumes to Provisioned IOPS SSD volumes.

Configure the IOPS Rate

Standard IOPS

If you do not select the Provision IOPS option when you create your M30+ tier cluster, the cluster uses standard IOPS. The default standard IOPS rate changes as the cluster's storage capacity changes. If you want to provision an exact IOPS value, enable provisioning.

The minimum standard IOPS for M30+ tier clusters is 3000. The standard IOPS value remains at 3000 unless you set the cluster storage size to 1TB or more. If the storage for your M30+ cluster meets or exceeds 1TB, Atlas increases the standard IOPS rate using an IOPS to storage ratio of 3:1.

Local NVMe SSD class clusters must use standard IOPS.

Provisioned IOPS

To provision IOPS for your M30+ tier 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 provisioned IOPS range for a cluster relates to disk storage capacity. Changing your cluster's storage capacity changes the range of available provisioned IOPS.

Minimum Disk Capacity to RAM Ratios

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

Instance sizes M10 to M40 have a ratio of disk capacity to system memory of 60:1. Instance sizes greater than M40 have a ratio of 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 a single replica set, regardless of cluster tier. To expand the total cluster storage beyond 4 TB, enable sharding.

Tip

Auto-Scale Cluster Tier and Storage Capacity

Note

Feature Availability

Atlas enables Cluster Auto-Scaling for all cluster tiers (except the highest cluster tier) under the General and the Low-CPU tier clusters.

For new clusters, Atlas automatically enables cluster tier auto-scaling and storage auto-scaling.

Use Auto-scale options to configure your cluster to automatically scale your {+cluster tier+}, storage capacity, or both in response to cluster usage.

Important

During a migration, if you restore a snapshot with a larger size than the storage capacity of the destination cluster, the cluster does not automatically scale.

You can opt out of cluster tier and storage autoscaling. To learn more, see How Atlas Scales Cluster Tier and How Atlas Scales Cluster Storage.

Tip