Azure Unmanaged Disks: A Practical Guide for Cloud Teams
Azure unmanaged disks have been a foundational option for virtual machines in Microsoft Azure. While the platform has largely moved toward managed disks for new deployments, unmanaged disks still appear in existing environments and offer a unique set of characteristics that matter for certain workloads. This guide provides a clear, human‑readable overview of what Azure unmanaged disks are, how they work, their advantages and tradeoffs, and practical guidance on when and how to use them—plus how to migrate away when you’re ready.
What are Azure unmanaged disks?
Azure unmanaged disks are virtual machine storage that lives as page blobs within an Azure Storage account. Each VM can have multiple disks, and each disk is stored as a blob in a storage account that you manage. The disks are created automatically when you provision a VM or attach additional data disks, and they persist independently of the VM’s lifecycle.
Because the disks reside in a storage account, they bring a different set of considerations compared with the newer Azure managed disks, where storage is abstracted away from the VM and managed by the platform. With Azure unmanaged disks, you are responsible for the storage account’s capacity, performance tier, replication, and other configuration decisions. This model can be appealing for teams that want explicit control over their storage layer or that need to work within constraints of established processes.
Key characteristics and implications
- Storage account dependency: All disks are stored in a specific storage account. This means that a VM’s disks are bounded by that account’s limits and performance characteristics.
- OS and data disks: Each VM has an OS disk and can attach multiple data disks, all stored as blobs in the same or multiple storage accounts depending on setup.
- Performance considerations: Performance depends on the storage account type (LRS, GRS, etc.) and the bandwidth of the associated blob storage. You must size and tune the storage account to match the workload needs.
- Management responsibilities: Administrators manage blob lifecycles, snapshots, redundancy, and backup strategies through storage accounts.
- Migration path: If you later decide to switch to managed disks, you can migrate to reduce operational overhead and simplify scaling.
Pros and cons at a glance
Understanding the tangible benefits and downsides helps teams decide when Azure unmanaged disks make sense.
- Cons: Higher operational overhead, potential storage account limits or throttling, limited integration with some modern platform features, and the recommended migration path toward Azure managed disks for new deployments.
How to use Azure unmanaged disks
Using Azure unmanaged disks involves coordinating the VM creation with an appropriate storage account. In practice, this means choosing a region, creating a storage account, and ensuring the account configuration aligns with your performance and redundancy requirements. From there, you provision VMs and attach OS and data disks that live in the selected storage account.
- Plan storage sizing and redundancy: Decide on the storage account type (standard or premium performance) and replication (LRS, ZRS, GRS) based on your data durability and latency requirements.
- Coordinate disk placement: Keep related disks in locality to minimize cross-region or cross-subnet latency when your VM uses multiple disks.
- Backup and snapshots: Leverage storage account snapshot capabilities to create point-in-time backups of your disks, and implement a retention policy aligned with your compliance needs.
- Monitoring: Use Azure Monitor and Storage metrics to track disk I/O, latency, and capacity consumption at the blob level to detect bottlenecks early.
Migration considerations: moving from unmanaged to managed disks
For teams planning a modernization path, migrating to Azure managed disks is often the recommended route. Managed disks simplify administration, offer improved scalability, and integrate more closely with Azure services. A typical migration involves creating new VMs with managed disks and transferring workloads or performing a disk-to-disk copy where supported by the environment. The migration process is incremental, allowing you to decommission the old unmanaged disks gradually while validating performance and reliability on the new managed disk infrastructure.
- Assessment: Inventory each VM that uses unmanaged disks, understand I/O patterns, and map storage accounts to the VMs that rely on them.
- Pilot migration: Start with non-critical workloads to validate migration steps, performance, and backup integration on managed disks.
- Phased transition: Move VMs one by one or in small batches, ensuring that dependencies (such as backup jobs or monitoring rules) are updated to point to managed disks.
- Decommission: After successful migration, remove the old unmanaged disks, purge the associated storage accounts if no longer needed, and update governance policies accordingly.
Performance, cost, and governance considerations
Choosing between Azure unmanaged disks and managed disks depends on workload characteristics and organizational policies. Some teams prioritize direct control over storage accounts, while others value streamlined operations and predictable scaling.
- Performance tuning: For Azure unmanaged disks, you may optimize latency and throughput by selecting appropriate storage account types and configuring VM IOPS expectations. Managed disks automatically scale IOPS based on disk size, reducing the need for manual tuning.
- Cost management: Unmanaged disks require careful cost governance for storage accounts, including replication, traffic, and access patterns. Managed disks simplify cost modeling by tying storage costs more directly to disk size and type.
- Security and access control: Storage accounts have their own access controls and shared access signatures. When using unmanaged disks, you must ensure that access is tightly governed to prevent unauthorized reads or tampering with your disks.
- Backup and DR alignment: Ensure that your backup and disaster recovery strategies are aligned with the storage account’s capabilities. With managed disks, backup and replication features are often more integrated and easier to manage centrally.
Security, compliance, and resiliency with unmanaged disks
Security posture for Azure unmanaged disks depends on the storage account configuration. Use strong authentication, restrict access with network rules, enable encryption at rest, and implement consistent monitoring for unusual activity. For compliance regimes that require strict data residency and auditability, you’ll want to document the storage account topology, blob lifecycle policies, and backup procedures clearly. Resiliency should consider multi-region replication and regular snapshot cycles to guard against data loss.
Real-world use cases and scenarios
There are legitimate scenarios where Azure unmanaged disks remain a practical choice. For example, organizations with legacy tooling or bespoke automation workflows built around storage accounts may continue to operate efficiently with unmanaged disks. In testing environments or migration sandboxes, you might begin with unmanaged disks to minimize upfront changes while you plan a broader transition to managed disks. Some teams also maintain a mixed environment, keeping new workloads on managed disks while preserving existing workloads on unmanaged disks until they complete their lifecycle.
Best practices for teams using Azure unmanaged disks today
- Document all storage dependencies: Maintain a clear map of which VMs rely on which storage accounts, and keep this in sync with deployment pipelines.
- Establish strict backup policies: Create regular snapshots and test restoration procedures to avoid surprises during incidents.
- Monitor proactively: Set up alerts for storage account capacity, blob latency, and VM disk I/O ceilings to prevent performance degradation.
- Plan for the future: Treat unmanaged disks as a stepping stone. Create a migration plan to managed disks with timelines, milestones, and validations.
Conclusion: choosing the right path for your cloud strategy
Azure unmanaged disks offer a direct, transparent approach to VM storage that can be suitable for certain legacy workflows or tightly controlled environments. However, for most new deployments and modern architectures, Azure managed disks provide easier management, better scalability, and tighter integration with the broader Azure ecosystem. If you’re starting a new project, lean toward managed disks. If you’re maintaining existing workloads, use Azure unmanaged disks with disciplined governance and a clear migration plan to managed disks when feasible. By balancing control with simplicity, you can ensure your cloud storage strategy aligns with your objectives, budgets, and risk tolerance while keeping Azure unmanaged disks aligned with practical, real-world needs.
