Azure Managed Disk reservations allow organizations to pre-purchase Premium SSD capacity at a discounted rate by committing to a one-year term. However, these reservations operate on a strict use-it-or-lose-it basis — if reserved disk capacity is not matched by provisioned disks in a given hour, that hour's reservation benefit is permanently lost and does not carry forward. This means that any mismatch between reserved quantities and actual disk deployment directly erodes the value of the commitment. Organizations commonly encounter this waste when workloads are decommissioned, migrated to different disk SKUs, or moved to different regions after the reservation was purchased.
A critical nuance is that disk reservations are purchased by specific SKU (such as P30 or P40), not by aggregate capacity. A P40 reservation cannot be applied to P30 disk usage, even though both are Premium SSDs. This SKU-level rigidity creates a significant mismatch risk: if an organization resizes disks or shifts workloads to a different tier, the original reservation provides zero benefit. Combined with the relatively modest discount that disk reservations offer compared to other Azure reservation types, even a small amount of underutilization can quickly eliminate any savings and turn the reservation into a net cost increase.
The cost impact compounds over time. Because unused reservation hours are permanently lost, an organization paying for reservations that consistently go partially or fully unused is effectively paying more than it would under standard pay-as-you-go pricing — the worst possible outcome for a commitment designed to save money.
For Premium SSD and Standard SSD disks 513 GiB or larger, Azure now offers the option to enable Performance Plus — unlocking higher IOPS and MBps at no extra cost. Many environments that previously required custom performance settings continue to pay for additional throughput unnecessarily. By not enabling Performance Plus on eligible disks, organizations miss a straightforward opportunity to reduce disk spend while maintaining or improving performance. The feature is opt-in and must be explicitly enabled on each qualifying disk.
Each Azure VM size has a defined limit for total disk IOPS and throughput. When high-performance disks (e.g., Premium SSDs with high IOPS capacity) are attached to low-tier VMs, the disk’s performance capabilities may exceed what the VM can consume. This results in paying for performance that the VM cannot access. For example, attaching a large Premium SSD to a B-series VM will not provide the expected performance because the VM cannot deliver that level of throughput. Without aligning disk selection with VM limits, organizations incur unnecessary storage costs with no corresponding performance benefit.
Workloads using legacy Premium SSD managed disks may be eligible for migration to Premium SSD v2, which delivers equivalent or improved performance characteristics at a lower cost. Premium SSD v2 decouples disk size from performance metrics like IOPS and throughput, enabling more granular cost optimization. Additionally, Premium SSD disks are often overprovisioned in size—for example, a P40 disk with more IOPS and capacity than the workload requires—resulting in inflated storage costs. Rightsizing includes both transitioning to v2 and resizing to smaller SKUs (e.g., P40 → P20) based on observed utilization. Failure to address either form of overprovisioning leads to persistent waste.
Standard SSD disks can often be replaced with Premium SSD v2 disks, offering enhanced IOPS, throughput, and durability at competitive or lower pricing. For workloads that require moderate to high performance but are currently constrained by Standard SSD capabilities, migrating to Premium SSD v2 improves both performance and cost efficiency without significant operational overhead.
Disks attached to VMs that have been stopped for an extended period, particularly when showing no read or write activity, may indicate abandoned infrastructure or obsolete resources. Retaining these disks without validation leads to unnecessary monthly storage costs. Reviewing and cleaning up inactive disks helps optimize spend and maintain storage hygiene.
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.
Managed Disks frequently remain detached after Azure virtual machines are deleted, reimaged, or reconfigured. Some may be intentionally retained for reattachment, backup, or migration purposes, but many persist unintentionally due to the lack of automated cleanup processes. When these detached disks are also inactive—showing no read or write activity—they represent unnecessary ongoing costs. Identifying and removing these orphaned disks can produce meaningful savings without affecting any active workloads.
