What does HRESULT 0xC038004D (ERROR_VOLMGR_NUMBER_OF_EXTENTS_INVALID) mean?

ERROR_VOLMGR_NUMBER_OF_EXTENTS_INVALID

Locate the rejected storage invariant: volmgr number of extents invalid

ERROR_VOLMGR_NUMBER_OF_EXTENTS_INVALID (0xC038004D) is emitted by the volmgr path when the extent count does not match the member and plex geometry represented in the layout buffer. The deciding object is logical volume geometry and the disk extents that realize it, so the first investigation belongs there rather than in a generic “disk failure” bucket.

Keep the first result attached to its request parameters and object instance. Cleanup failures or a later drive-letter change are secondary evidence, not replacements for the original failure.

Evidence to preserve before repair

One-variable reproduction

1. Capture the API parameters and object map that led to this result; do not begin with cleanup.
2. Build a passing control with the same disks or image copy and preserve volume ID, requested length, sector sizes, extent table, plex/member counts, disk health and the exact VM_VOLUME_LAYOUT buffer.
3. Run the narrow transition described here: serialize the exact VM_VOLUME_LAYOUT buffer, validate every count and Size field, and compare it with a layout produced by a known-good management API.
4. Compare resulting IDs, counts, health and ownership to prove the caller crossed the result invariant rather than suppressing it.

Use ERROR_VOLMGR_UNEXPECTED_DISK_LAYOUT_CHANGE as the nearest comparison. It is specific to the extent count does not match the member and plex geometry represented in the layout buffer; the neighboring result belongs to another validation or lifecycle branch. Keeping both names prevents a generic storage label from hiding the actual owner.

Mechanism-specific note

The count field is part of the layout contract rather than an advisory value. Verify it against the number of serialized descriptors and against the minimum geometry required by the selected layout type. Check multiplication and addition for overflow before allocating or copying the variable-length buffer, because a correctly sized allocation can still contain a logically impossible count.

Repair without rewriting unrelated metadata

Rebuild the layout from enumerated objects and checked arithmetic rather than patching one serialized field; validate counts, indices, sizes, alignment and overflow before submission. Keep the correction scoped to the owning object and avoid rewriting adjacent metadata merely to make the call return success.

• The original request now reaches success or a documented later status with the intended layout and access mode.
• A new enumeration reports internally consistent IDs, counts, geometry and ownership for the corrected object.
• The application still distinguishes it from ERROR_VOLMGR_UNEXPECTED_DISK_LAYOUT_CHANGE and has no unbounded retry loop.

Technical references

• Microsoft: COM error codes for VOLMGR, VHD and SDIAG — defines the volmgr objects used to interpret it.
• Microsoft: Virtual Disk Service object model — primary API or object-model reference.
• Microsoft: Pack object — use this source to verify volmgr state and parameters.
• Microsoft: Virtual Disk Service common return codes — documents the supported management path relevant to this HRESULT.