What does HRESULT 0xC038002D (ERROR_VOLMGR_NUMBER_OF_MEMBERS_INVALID) mean?

ERROR_VOLMGR_NUMBER_OF_MEMBERS_INVALID

Identify the owner before touching the layout: volmgr number of members invalid

The practical meaning of ERROR_VOLMGR_NUMBER_OF_MEMBERS_INVALID (0xC038002D) is tied to dynamic-volume plex member descriptor and its backing extents: the plex layout declares a member count that is incompatible with its plex type or supplied member descriptors. The result does not, by itself, prove file-system corruption or physical-media failure.

A useful record contains more than the final UI symptom: retain the first failing call, target identity, topology and state transition before management software rescans the disks.

Minimum diagnostic set

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

Reproduce without destructive cleanup

1. Associate this result with one caller, one transaction and one target UniqueId.
2. Save the pre-call and post-call inventories, including pack ID, volume ID, plex index, member index, disk IDs, extent offsets, health state and regeneration percentage.
3. Use this A/B case without touching unrelated storage: 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. Validate both the HRESULT and the on-disk or provider state after the relevant reopen, remount or attach cycle.

A useful diagnostic fork is ERROR_VOLMGR_UNEXPECTED_DISK_LAYOUT_CHANGE versus it. This code concerns the plex layout declares a member count that is incompatible with its plex type or supplied member descriptors; the alternate code should remain observable after the fix, proving the application did not suppress the entire subsystem.

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.

Restore the contract

Rebuild the layout from enumerated objects and checked arithmetic rather than patching one serialized field; validate counts, indices, sizes, alignment and overflow before submission. The repair is incomplete until a fresh enumeration and new handle observe the corrected state.

• 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_VOLMGR_UNEXPECTED_DISK_LAYOUT_CHANGE path remains separately testable and separately logged.

Technical references

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