Count disk reservation demand by SKU rather than pooled capacity

Source facts

Microsoft explains that a disk reservation is consumed by matching disk SKU units, not by a pool of provisioned capacity. Its example shows that a P40 reservation does not cover two P30 disks. Reservation discounts apply hourly, and unused reserved capacity does not carry forward. Microsoft Learn

Applicability

This is a technical inventory check for an Azure Disk Storage reservation review, where the team is comparing actual disk SKUs with proposed reservation quantities.

DSE recommendation

DSE recommends preparing a disk-by-disk inventory grouped by the exact eligible SKU and intended reservation scope. Separate steady demand from temporary or uncertain usage and document anticipated changes in disk type. Have the resource owner reconcile the inventory before anyone proposes a reservation quantity. Keep pricing, purchase authorization, and commercial suitability in the organization’s normal financial review rather than inferring a commitment from total terabytes.

Verification

Compare each inventory row with the current disk properties and verify that SKU quantities reconcile with the proposed coverage. Mark unmatched disks and uncertain usage explicitly. After an authorized purchase, use observed reservation application to check the mapping and investigate discrepancies; do not describe unverified savings as a result.

Official references

• Microsoft: Optimize costs for Azure Disk Storage with reservations – Azure Virtual Machines | Microsoft Learn