This implies that or another mechanism changed the block between when Process A last checked it and when the atomic operation executed. 3. Common Causes and Scenarios
In a shared storage environment, multiple server nodes (ESXi hosts) read and write to the same logical unit number (LUN) or datastore. To prevent data corruption, a host must secure a lock before modifying metadata (e.g., creating a file, extending a virtual disk, or updating a heartbeat).
Under extreme storage load, the time it takes for an ATS command to travel from the host to the array increases. If the host takes too long to execute the operation, another host may swoop in, modify the metadata first, and complete its write. When the first host's delayed command finally reaches the disk, the on-disk state has changed, causing an instant miscompare. B. Out-of-Sync Firmware and Multipathing Glitches This implies that or another mechanism changed the
The issue can also be traced to the ESXi host's own hardware or software stack:
While correct, a false result triggers specific behavioral patterns in software: To prevent data corruption, a host must secure
A node caches disk block values but fails to invalidate the cache after a write from another node. Result: The node issues a test-and-set based on stale data, causing an unexpected failure. Solution: Disable aggressive caching for shared block devices; use O_DIRECT or O_SYNC where appropriate.
This cryptic error message emerges from the heart of VMware's advanced storage integration, specifically pointing to a problem with a mechanism used to maintain data integrity. Understanding why a simple equality test fails requires exploring the layers of a modern virtualized data center, from the hypervisor's filesystem down to the storage array's firmware. When the first host's delayed command finally reaches
Check your storage performance metrics. Look for spikes in device latency and kernel latency. If your HBA queue depths are set too low, commands will back up at the operating system level, delaying the execution of the ATS command and causing it to fail the equality check. Consider tuning host queue depths according to your storage vendor's recommendations. Step 3: Update Firmware and Drivers Ensure that the entire data path is up to date:
: If another host successfully updated the block metadata just milliseconds before, the original host's "expected" data is now stale, triggering the miscompare.
Verify all Fibre Channel/iSCSI HBAs are using the drivers and firmware listed in the VMware Compatibility Guide.
Typical atomic TAS on disk block: