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Learn about ONTAP capacity balancing in an ASA r2 cluster

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For ASA r2 systems, ONTAP uses balanced placement to automatically place newly created storage units in the best storage availability zone for optimal performance and balanced storage utilization. If you are running ONTAP 9.17.1 or later, space consumed by existing storage units is balanced using dynamic space balancing. If you are running ONTAP 9.16.1, space consumed by existing storage units is balanced using copy-based workload rebalancing.

Feature Supported in…​

Balanced placement

ONTAP 9.16.1 and later

Dynamic space balancing

ONTAP 9.17.1 and later

Copy-based workload rebalancing

ONTAP 9.16.1 only
Balanced placement

With balanced placement, newly created storage units are automatically placed within the best storage availability zone for optimal performance and balanced storage utilization. Balanced placement is enabled by default in ONTAP 9.16.1 and later.

Dynamic space balancing

With dynamic space balancing, ONTAP actively monitors the amount of free space in the cluster and automatically moves storage units within storage availability zones to maintain balanced space utilization. An EMS warning is automatically issued if cluster-wide capacity utilization reaches 80% and an EMS alert is automatically issued if it reaches 90%.

Dynamic space balancing is enabled by default 14 days after upgrading to or installing ONTAP 9.17.1 or later. If you need to modify the default 14-day enablement period, contact NetApp Support. You cannot revert from ONTAP 9.17.1 after dynamic space balancing is enabled.

Dynamic space balancing operates in either normal mode or low space mode based on the overall average of free space in all nodes in the cluster (global average).

  • Normal mode

    In normal mode, ONTAP checks every three minutes to determine if dynamic space balancing is needed. Dynamic space balancing operates in normal mode when the following conditions are true:

    • The global average for free space is 10% or more.

    • At least one node in the cluster has more free space than the global average.

    • At least one node in the cluster has 20% less free space than the global average.

  • Low space mode

    In low space mode, ONTAP checks every minute to determine if dynamic space balancing is needed. Dynamic space balancing operates in low space mode when the following conditions are true:

    • The global average for free space is less than 10%.

    • At least one node in the cluster has more free space than the global average.

    • At least one node in the cluster has less free space than the global average.

Copy-based workload rebalancing

With copy-based workload rebalancing, if an imbalance in storage utilization occurs within the storage availability zones, ONTAP automatically copies the storage unit creating the imbalance to a storage availability zone with greater free space. If there is not enough free space in the destination storage availability zone, ONTAP does not perform any balancing action. Copy-based workload rebalancing applies only to ASA r2 system running ONTAP 9.16.1, and it is enabled by default on those systems. In ONTAP 9.17.1 and later, it is replaced with dynamic space balancing.

If you need to modify the default settings for copy-based workload rebalancing, contact NetApp Support.