When the ONTAP software's background scanner or a read operation detects a logical or structural problem within the WAFL (Write Anywhere File Layout) file system on an aggregate, it triggers a critical Event Management System (EMS) event. The specific event for this condition is wafl.inconsistent.block. By default, this critical event is configured to automatically generate and send a "WAFL INCONSISTENT BLOCK" AutoSupport message to NetApp support. This message alerts administrators and support personnel to a potential file system corruption issue that requires immediate investigation.

A. MEDIUM ERROR DURING RECONSTRUCTION: This message is triggered by a RAID-level event (raid.rg.recons.mediumerror) when a disk encounters read errors during a parity reconstruction, not a WAFL file system inconsistency.

B. CHECKSUM ERROR: While a checksum error can be a symptom of an inconsistency, the specific AutoSupport for it is typically related to the wafl.raid.cksum.mismatch event, which is distinct from a general WAFL structural inconsistency.

C. WAFL INCONSISTENT USER DATA BLOCK: This is not the standard name for the AutoSupport message. The official event wafl.inconsistent.block is more general and covers inconsistencies in both user data and metadata blocks.

1. NetApp ONTAP 9.12.1 EMS event catalog:

Event Name: wafl.inconsistent.block

Description: "WAFL has detected an inconsistent block. This can be a result of a software error or a hardware problem that was not properly detected."

Default Action: This event is classified as severity "CRITICAL" and is configured by default to trigger an AutoSupport notification.

(This official catalog directly links the condition described in the question to the correct answer.)

2. NetApp Technical Report TR-4742: Block Checksums in ONTAP:

Section: "How ONTAP Detects and Corrects Corrupt Data"

Content: The document explains various data protection mechanisms. It differentiates between checksum mismatches (data corruption) and WAFL inconsistencies (file system structural errors). The background WAFL scanner is described as the process that finds inconsistencies, which would trigger the wafl.inconsistent.block event and a corresponding AutoSupport message.

(This source clarifies the distinction between a checksum error (Option B) and a broader WAFL inconsistency.)