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Node-specific Volume Limits

This page describes the maximum number of volumes that can be attached to a Node for various cloud providers.

Cloud providers like Google, Amazon, and Microsoft typically have a limit on how many volumes can be attached to a Node. It is important for Kubernetes to respect those limits. Otherwise, Pods scheduled on a Node could get stuck waiting for volumes to attach.

Kubernetes default limits

The Kubernetes scheduler has default limits on the number of volumes that can be attached to a Node:

Cloud serviceMaximum volumes per Node
Amazon Elastic Block Store (EBS)39
Google Persistent Disk16
Microsoft Azure Disk Storage16

Custom limits

You can change these limits by setting the value of the KUBE_MAX_PD_VOLS environment variable, and then starting the scheduler.

Use caution if you set a limit that is higher than the default limit. Consult the cloud provider’s documentation to make sure that Nodes can actually support the limit you set.

The limit applies to the entire cluster, so it affects all Nodes.

Dynamic volume limits

FEATURE STATE: Kubernetes v1.12 beta
This feature is currently in a beta state, meaning:

  • The version names contain beta (e.g. v2beta3).
  • Code is well tested. Enabling the feature is considered safe. Enabled by default.
  • Support for the overall feature will not be dropped, though details may change.
  • The schema and/or semantics of objects may change in incompatible ways in a subsequent beta or stable release. When this happens, we will provide instructions for migrating to the next version. This may require deleting, editing, and re-creating API objects. The editing process may require some thought. This may require downtime for applications that rely on the feature.
  • Recommended for only non-business-critical uses because of potential for incompatible changes in subsequent releases. If you have multiple clusters that can be upgraded independently, you may be able to relax this restriction.
  • Please do try our beta features and give feedback on them! After they exit beta, it may not be practical for us to make more changes.

Kubernetes 1.11 introduced support for dynamic volume limits based on Node type as an Alpha feature. In Kubernetes 1.12 this feature is graduating to Beta and will be enabled by default.

Dynamic volume limits are supported for following volume types.

  • Amazon EBS
  • Google Persistent Disk
  • Azure Disk
  • CSI

When the dynamic volume limits feature is enabled, Kubernetes automatically determines the Node type and enforces the appropriate number of attachable volumes for the node. For example:

  • On Google Compute Engine, up to 128 volumes can be attached to a node, depending on the node type.

  • For Amazon EBS disks on M5,C5,R5,T3 and Z1D instance types, Kubernetes allows only 25 volumes to be attached to a Node. For other instance types on Amazon Elastic Compute Cloud (EC2), Kubernetes allows 39 volumes to be attached to a Node.

  • On Azure, up to 64 disks can be attached to a node, depending on the node type. For more details, refer to Sizes for virtual machines in Azure.

  • For CSI, any driver that advertises volume attach limits via CSI specs will have those limits available as the Node’s allocatable property and the Scheduler will not schedule Pods with volumes on any Node that is already at its capacity. Refer to the CSI specs for more details.

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