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ERROR_VOLMGR_PLEX_LAST_ACTIVE
What this result says about the disk model: volmgr plex last active
ERROR_VOLMGR_PLEX_LAST_ACTIVE (0xC038003B) is emitted by the volmgr path when removing the selected plex would leave the volume without any active data copy. The deciding object for it is volume plex descriptor, layout type and regeneration state, so the first investigation belongs there rather than in a generic “disk failure” bucket.
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 while diagnosing it.
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.
Capture the exact object generation
| Storage diagnostic field | Value |
|---|---|
| Identity and generation | volume ID, plex ordinal, plex type, member array, active/inactive state, health status and current regeneration job |
| Narrow experiment | 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 |
| Closest comparison | ERROR_VOLMGR_UNEXPECTED_DISK_LAYOUT_CHANGE |
| Owning object | volume plex descriptor, layout type and regeneration state |
| Rejected invariant | removing the selected plex would leave the volume without any active data copy |
Do not overwrite this result with a close, detach or rollback error. Preserve the causal order so the original storage contract remains visible.
Prove the boundary in a test volume
- Associate this result with one caller, one transaction and one target UniqueId while diagnosing it.
- Save the pre-call and post-call inventories, including volume ID, plex ordinal, plex type, member array, active/inactive state, health status and current regeneration job.
- Use this A/B case for it 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 for it.
- Validate both the HRESULT and the on-disk or provider state after the relevant reopen, remount or attach cycle for it.
Compare traces for ERROR_VOLMGR_UNEXPECTED_DISK_LAYOUT_CHANGE and this result. The latter page covers a nearby storage boundary, whereas it rejects removing the selected plex would leave the volume without any active data copy. A correct caller should be able to reproduce each case independently.
Mechanism-specific note
The selected plex is the last data-bearing path for the volume. Before detaching it, identify another active copy and verify that it is readable and synchronized. Administrative intent to delete the volume is a separate workflow; a maintenance API must not infer that intent from a request to remove one plex.
Safe recovery path
Select an operation compatible with the actual plex type and keep at least one active data copy throughout detach, repair or regeneration for it. Apply the change through the supported storage API, then close and reacquire affected objects before retrying.
- The controlled A/B case changes only the invariant responsible for it.
- No unrelated disk, cluster owner, tier policy or virtual-disk backing file is altered to hide it.
- Health, synchronization or job state reaches a terminal value consistent with the repaired the operation.
- Telemetry includes both symbolic names when it or
ERROR_VOLMGR_UNEXPECTED_DISK_LAYOUT_CHANGEoccurs again.
Do not use it as a reason to edit dynamic-disk sectors, VHDX metadata, RCT sidecars or snapshot support files directly. Unsupported edits can turn a recoverable state mismatch into persistent corruption.
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 for the boundary.
- Microsoft: Pack object — use this source to verify volmgr state and parameters for it.
- Microsoft: Virtual Disk Service common return codes — documents the supported management path relevant to it.
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