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VSS_E_ASRERROR_DYNAMIC_VHD_NOT_SUPPORTED
VSS_E_ASRERROR_DYNAMIC_VHD_NOT_SUPPORTED is the failure HRESULT 0x8004240A (signed decimal -2147212278, unsigned decimal 2147755018). Its severity bit is set, the facility field is 4 (FACILITY_ITF), and the facility-specific code is 0x240A.
A critical dynamic disk is a virtual hard disk. The critical disk selected for Automated System Recovery is a VHD using dynamic-disk organization. AllStat explicitly classifies this combination as unsupported.
AllStat records the official condition as: “A critical dynamic disk is a Virtual Hard Disk (VHD). This is an unsupported configuration. Check the Application event log for more details.” This wording should be interpreted at the VSS/ASR stage described below, not as a generic disk or COM failure.
Where VSS_E_ASRERROR_DYNAMIC_VHD_NOT_SUPPORTED appears
The ASR writer detects the disk type while building or validating critical-disk metadata. The operation stops before a reliable bare-metal backup or restore plan can be formed.
Likely causes
- A boot-critical volume resides on a VHD that Windows also manages as a dynamic disk.
- A virtualized recovery design converts a previously supported basic disk to dynamic organization.
- The backup scope includes a mounted VHD that has become critical to system startup or system state.
- Automation assumes that VHD support and dynamic-disk support imply support for their combination.
Evidence to capture before changing storage
- Identify the critical volume, backing VHD path or attachment, and dynamic-disk group.
- Capture disk type, virtual-disk type and the reason the volume is considered critical.
- Check the VSS Application event named by the AllStat description.
- Document whether the VHD is a host artifact, guest disk or locally mounted image.
Diagnostic sequence
- Confirm both predicates: the disk is virtual and its Windows disk organization is dynamic.
- Determine whether the volume truly belongs in the ASR critical set.
- Review whether the system can be redesigned onto supported basic storage before the next backup.
- Do not infer that changing only VHD allocation mode, such as fixed versus expanding, removes the dynamic-disk restriction.
Recovery and retry
Move critical system content to a supported disk configuration or use a documented alternative recovery mechanism for that virtualized topology. Retry after creating a new backup whose critical-disk metadata no longer contains the unsupported combination.
What this HRESULT does not prove
The HRESULT does not say the VHD file is corrupt, detached or full. A healthy attached VHD can still be unsupported because it is a critical dynamic disk.
Difference from nearby VSS results
VSS_E_CRITICAL_VOLUME_ON_INVALID_DISK is the broader invalid-hosting-disk result. This value identifies the dynamic-VHD combination exactly.
Practical example
A machine boots from a mounted VHD whose disk was converted to dynamic to add another extent. ASR discovers the critical virtual dynamic disk and refuses to advertise a supported disaster-recovery backup.
Guidance for backup software and telemetry
Surface the storage combination and affected critical volume in product validation before backup starts. Discovering it only during disaster recovery leaves no safe automatic fix.
A useful support record includes the operation phase, backup set or restore session identifier, recovery-environment version, firmware mode, exact disk identities, source and target capacities, online/exclusion state, and the first related VSS or storage event. Preserve identifiers needed to distinguish the affected devices while applying the organization’s normal redaction rules to customer-specific labels and paths.
Official Microsoft references
- Microsoft: VSS Automated System Recovery for disaster recovery
- Microsoft: manage virtual hard disks
- Microsoft: basic and dynamic disks
- Microsoft: the VSS requester, writer and provider model
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