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VDS_E_INVALID_EXTENT_COUNT
A disk extent is a contiguous byte range on one disk or LUN. VDS uses extents as the physical building blocks beneath volumes, plexes, and members. The count matters because particular operations impose structural rules on how many extents a disk may contribute. The most obvious example is the one-extent-per-disk rule for calls that require one extent for each contributing disk member.
Why this state matters
This HRESULT should lead to an extent map, not a file-system scan. Query the disk and plex extents and group them by disk ID, volume ID, plex ID, and member index. If the layout changed outside the current client, a previously valid count can become stale. Also inspect the request builder for accidentally emitting zero-length or duplicated extent records before blaming the provider cache.
Diagnostic focus
- Collect
VDS_DISK_EXTENTrecords for every contributing disk and the current plex. - Count extents per disk and per member, preserving offset and size for duplicate detection.
- Compare the actual topology with the exact method requirement instead of assuming every VDS call accepts fragmented contribution.
- Requery after external layout changes so an old extent count is not mixed with a new disk map.
Technical references
VDS_DISK_EXTENT · IVdsDisk::QueryExtents · IVdsVolumePlex::QueryExtents · MS-VDS storage object relationships · Disk Object
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