Managed Disk Attached to a Deallocated VM

Service Category

Storage

Cloud Provider

Azure

Service Name

Azure Managed Disks

Inefficiency Type

Unused Resource

Explanation

This inefficiency occurs when a VM is deallocated but its attached managed disks are still active and incurring storage charges. While compute billing stops for deallocated VMs, the disks remain provisioned and billable. These disks often persist unintentionally after a VM is paused, retired, or left unused in dev/test environments, resulting in waste if not explicitly cleaned up.

Relevant Billing Model

Managed Disks are billed per GB of provisioned size, regardless of usage or attachment state. Disks continue to incur costs even when their associated VM is deallocated. Additional charges may apply for features such as disk snapshots, premium performance tiers, or zone-redundant storage.

Detection

Identify managed disks attached to deallocated VMs during the defined lookback period
Review disk activity to confirm no read/write operations occurred while the VM was deallocated
Evaluate whether the disk is still needed for backup, migration, or future reactivation
Check whether the VM and disk are associated with an active project or retired environment
Confirm with owners or stakeholders whether the data must be retained or can be removed

Remediation

Delete managed disks that are no longer needed. If data may be needed in the future, take a snapshot or export the disk before deletion. Establish regular cleanup processes to review disks attached to deallocated VMs. Automate tagging and audit routines to flag idle resources for follow-up.

Relevant Documentation