What does HRESULT 0xC03A001D (ERROR_VIRTDISK_UNSUPPORTED_DISK_SECTOR_SIZE) mean?

ERROR_VIRTDISK_UNSUPPORTED_DISK_SECTOR_SIZE

Read the code at the owning storage layer: virtdisk unsupported disk sector size

ERROR_VIRTDISK_UNSUPPORTED_DISK_SECTOR_SIZE has unsigned value 0xC03A001D. In the virtdisk layer, the operation is rejected because the host storage sector geometry is not supported for the virtual disk format or requested attach/create operation. Diagnosis should follow Virtual Disk API provider, image format and host-disk state through one controlled state transition.

The Virtual Disk API chooses a format provider from VIRTUAL_STORAGE_TYPE, opens an image with explicit access rights and can attach it as a disk. Provider selection, backing-chain integrity, host-file attributes, sector geometry and operating-system ownership are independent validation stages.

Build a trustworthy incident record

Do not overwrite this result with a close, detach or rollback error. Preserve the causal order so the original storage contract remains visible.

Controlled comparison

1. Associate this result with one caller, one transaction and one target UniqueId.
2. Save the pre-call and post-call inventories, including image path, VIRTUAL_STORAGE_TYPE, provider/vendor IDs, VHD/VHDX/VHD Set identifiers, host sector sizes, attach flags, ownership and online/read-only state.
3. Use this A/B case without touching unrelated storage: move a copy of the image between host disks with documented sector geometries and repeat the same create or attach operation.
4. Validate both the HRESULT and the on-disk or provider state after the relevant reopen, remount or attach cycle.

The distinction from ERROR_VIRTDISK_NOT_VIRTUAL_DISK is operational. The host storage sector geometry is not supported for the virtual disk format or requested attach/create operation; log the neighboring code separately so capability, identity and state are not conflated.

Mechanism-specific note

Record logical and physical sector sizes for every layer: image format, host file system and physical disk. Alignment must be checked with integer arithmetic before truncation. Copying an image to a different device can change the host geometry even when the image bytes and virtual capacity remain identical.

Completion criteria

Correct the provider, image format, backing-file chain, host geometry or disk ownership identified by the failing call, then reopen the image to obtain a new handle before retrying. Keep the correction scoped to the owning object and avoid rewriting adjacent metadata merely to make the call return success.

• the first retry uses newly enumerated identifiers rather than cached handles.
• The durable metadata or provider state agrees with the success returned after it.
• A second run after close/reopen does not recreate the rejected condition.
• the nearby ERROR_VIRTDISK_NOT_VIRTUAL_DISK path remains separately testable and separately logged.

Technical references

• Microsoft: Virtual Disk API — documents the supported management path relevant to this HRESULT.
• Microsoft: OpenVirtualDisk — defines the virtdisk objects used to interpret it.
• Microsoft: AttachVirtualDisk — primary API or object-model reference.
• Microsoft: GetVirtualDiskInformation — use this source to verify virtdisk state and parameters.