What does HRESULT 0xC038003A (ERROR_VOLMGR_PLEX_INDEX_INVALID) mean?

ERROR_VOLMGR_PLEX_INDEX_INVALID

Read the code at the owning storage layer: volmgr plex index invalid

ERROR_VOLMGR_PLEX_INDEX_INVALID has unsigned value 0xC038003A. In the volmgr layer, the operation is rejected because a plex ordinal is outside the plex count declared for the volume. Diagnosis of this result should follow volume plex descriptor, layout type and regeneration state through one controlled state transition.

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Controlled comparison

1. Create a nonproduction case that preserves the same geometry and ownership model.
2. Collect volume ID, plex ordinal, plex type, member array, active/inactive state, health status and current regeneration job before invoking the first mutating API.
3. Change one condition only: hold the descriptor count fixed and compare the boundary ordinal with the first value outside the valid range.
4. Re-enumerate after the transition and confirm it is not reproduced by a stale handle from the old generation.

ERROR_VOLMGR_PLEX_INDEX_DUPLICATE describes a nearby but different storage condition; this result indicates that a plex ordinal is outside the plex count declared for the volume.

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.

Completion criteria

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 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_PLEX_INDEX_DUPLICATE path remains separately testable and separately logged.

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.