What does HRESULT 0xC0380025 (ERROR_VOLMGR_MEMBER_INDEX_INVALID) mean?

ERROR_VOLMGR_MEMBER_INDEX_INVALID

Why this is narrower than a generic disk error: volmgr member index invalid

ERROR_VOLMGR_MEMBER_INDEX_INVALID has unsigned value 0xC0380025. In the volmgr layer, the operation is rejected because a member ordinal lies outside the member array declared for the selected plex. Diagnosis of this result should follow dynamic-volume plex member descriptor and its backing extents through one controlled state transition.

Diagnosis of this result should begin with the object model and generation current at the failure. A later successful enumeration may describe a replacement object and cannot retroactively validate the rejected request.

Storage facts that change the diagnosis

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

A/B test

1. Before changing state, freeze the failing generation and save pack ID, volume ID, plex index, member index, disk IDs, extent offsets, health state and regeneration percentage.
2. Exercise this exact comparison: hold the descriptor count fixed and compare the boundary ordinal with the first value outside the valid range.
3. During the comparison, keep image bytes, unrelated disks, provider policy and cluster topology fixed.
4. After the test, record the next return value and the durable object state; crossing the boundary should expose a later result rather than silently retrying.

ERROR_VOLMGR_MEMBER_INDEX_DUPLICATE describes a nearby but different storage condition; this result indicates that a member ordinal lies outside the member array declared for the selected plex.

Mechanism-specific note

Treat the ordinal as a generation-scoped array index. Record the declared count, the rejected index and whether the object list was refreshed between enumeration and submission. An index that was valid before a disk rescan can become out of range even though the corresponding disk, member or plex still exists under a stable identifier.

Corrective action and regression check

Rebuild the layout from enumerated objects and checked arithmetic rather than patching one serialized field; validate counts, indices, sizes, alignment and overflow before submission. Apply the change through the supported storage API, then close and reacquire affected objects before retrying.

• 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 passing state survives the relevant lifecycle transition, such as reopen, remount, owner change or detach/attach.
• The application still distinguishes it from ERROR_VOLMGR_MEMBER_INDEX_DUPLICATE and has no unbounded retry loop.

Technical references

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