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ERROR_SVHDX_UNIT_ATTENTION_OPERATING_DEFINITION_CHANGED
A device definition changed beneath the initiator
ERROR_SVHDX_UNIT_ATTENTION_OPERATING_DEFINITION_CHANGED reports a Unit Attention condition in which the data-storage definition seen by the initiator changed. It is a compatibility and state-revalidation signal. It should not be reduced to a generic disk-read failure, and it does not identify a single cause such as a damaged VHDX file.
For a shared virtual disk, the visible storage definition can depend on the server-side virtual-disk implementation, negotiated protocol behavior, disk attachment state, and the device characteristics presented to consumers. Software that cached capacity, block-related assumptions, reservation state, or protocol capabilities before the change should refresh them before continuing a sequence that relies on the old definition.
Investigation points
- Capture the associated SCSI sense data and determine whether another, more specific Unit Attention reason is also reported.
- Compare the virtual-disk configuration and server version before and after the event, including recent storage migration, replacement, or maintenance actions.
- Revalidate the disk identity and current capacity rather than assuming that the same path refers to an unchanged logical unit.
- For a shared-cluster disk, confirm current registrations and reservation ownership before any write, metadata update, or recovery action.
What not to do
Do not attempt to clear the condition by manually changing VHDX files, forcing a disk online, or reissuing write requests from every guest. The Unit Attention is a state-change notification; uncontrolled retries can race the component that is legitimately reconstructing the shared-disk view.
References
- Microsoft Open Specifications: Remote Shared Virtual Disk Protocol
- T10: SCSI changed-state and reservation semantics
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