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, it rejects a specific contract because a plex ordinal is outside the plex count declared for the volume for it. Diagnosis of this result should follow volume plex descriptor, layout type and regeneration state through one controlled state transition.

Dynamic volumes are represented as packs containing disks and volumes; each volume has one or more plexes, and each plex is assembled from members and extents. Indices and counts are relative to the submitted layout generation, while configuration logs are replicated across participating dynamic disks while diagnosing this result. This object model determines which identifiers, counts and ownership state are meaningful for it.

The standard message identifies the immediate condition, but this result also requires the producer API, object topology and attempted state transition for it. Capture them before an automatic refresh advances the storage generation.

Build a trustworthy incident record

Keep this HRESULT as the primary result if rollback or cleanup reports another code; those later values describe recovery, not the first rejected invariant for it.

Controlled comparison

1. Create a nonproduction case for it that preserves the same geometry and ownership model while diagnosing this result.
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 while diagnosing it.
4. Re-enumerate after the transition and confirm it is not reproduced by a stale handle from the old generation.

Compare traces for ERROR_VOLMGR_PLEX_INDEX_DUPLICATE and it. The latter page covers a nearby storage boundary, whereas it rejects a plex ordinal is outside the plex count declared for the volume while diagnosing it. A correct caller should be able to reproduce each case independently for it.

Mechanism-specific note

Treat the ordinal as a generation-scoped array index for it. 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 while diagnosing it.

• 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 the condition.
• the nearby ERROR_VOLMGR_PLEX_INDEX_DUPLICATE path remains separately testable and separately logged.

A reboot, blanket disk conversion or deletion of storage metadata is not a justified first response to it; it changes multiple invariants and can erase the evidence needed to identify the defect.

Technical references

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

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