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VDS_E_VD_NOT_ATTACHED_READONLY
This status expresses an attachment-mode precondition rather than a generic read-only file error. VDS attach accepts ATTACH_VIRTUAL_DISK_FLAG_READ_ONLY, and some virtual-disk maintenance operations require the disk to be detached or attached read-only. DiskPart documents the same constraint for compacting dynamically expanding VHDs.
Why this state matters
A disk that is attached read/write does not satisfy the condition just because no application is currently writing to it. The access mode is part of the attachment established through the virtual-disk API. Diagnostics should inspect how the disk was attached and coordinate a controlled detach/reattach if a maintenance operation truly requires read-only exposure.
Diagnostic focus
- Identify the operation that returned the HRESULT and verify its documented attachment-mode requirement.
- Check the flags used when the current attachment was created instead of inferring mode from observed I/O activity.
- Coordinate users of the disk before changing attachment mode; read-only reattachment is a topology and access change.
- After detaching, reopen and attach with the documented read-only flag, then retry only the operation that requires that mode.
Technical references
IVdsOpenVDisk::Attach · IVdsOpenVDisk::Compact · compact vdisk command · VDS_VDISK_STATE · IVdsOpenVDisk
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