Managed Disks¶

Recommendation types¶

Terminate¶

Fires when a disk is unattached or attached to a deallocated VM (Azure disk state Reserved). In both cases the disk bills its full provisioned capacity while serving no active workload.

• Unattached: fires immediately, with no minimum observation period.
• Reserved: fires because the VM is deallocated, but the engine also checks whether a cheaper disk tier qualifies. When both a rightsize and a terminate candidate exist, rightsize is the primary recommendation (less aggressive: keep the disk, move it to a cheaper tier) and terminate is stored as an alternative inside the recommendation evidence (more aggressive: delete the disk). Teams that turn the VM on occasionally will prefer the rightsize path; teams that have permanently stopped the VM can act on terminate instead.

Rightsize¶

Fires for attached disks (and Reserved disks with sufficient metric history) whose observed IOPS and throughput sit well below what their current tier provisions. The engine recommends the cheapest tier that would still cover the observed load with the configured headroom margin.

Thresholds¶

Why the default is 20%¶

The metrics collector queries Azure Monitor at one-hour granularity (PT1H) and stores the peak hourly average per day. This means the baseline already reflects intra-day burst behaviour rather than a smoothed daily average. A disk that runs checkpoint writes for 30 minutes per hour will show that burst in the stored peak value.

20% headroom above an observed hourly peak provides a practical safety margin without requiring excessive over-provisioning. It accounts for natural variation between days and for brief sub-hourly spikes that the one-hour window does not fully capture.

If your disks serve workloads with sharp, irregular bursts shorter than one hour — for example, batch jobs that complete in minutes — raise the headroom to 40–60% before acting on rightsize recommendations. For steady or predictable workloads, 20% is appropriate.

Auto-implementation¶

The engine detects implementation automatically on each run. Detection applies to any recommendation in the In Review, Planned, Snoozed, or Ignored status. A team member may act on a recommendation that was not formally planned, and those savings are captured regardless of what status the recommendation was in at the time.

• Terminate: when the disk's inventory status changes to Deleted, the recommendation is marked implemented.
• Rightsize: when the current disk tier in inventory matches the recommended tier, the recommendation is marked implemented.