Atomic Test And Set Of Disk Block Returned False For Equality
In a highly dynamic cluster, multiple hosts frequently attempt to modify the same volume simultaneously (e.g., during mass virtual machine power-ons, migrations, or snapshot creations). If Host A and Host B both read a metadata block at the same time, Host A may successfully execute its ATS write first. When Host B attempts its ATS write milliseconds later, the metadata has changed. Host B’s "Test" phase fails because the disk block no longer matches its outdated cache. 2. Storage Path Flapping and Multipathing Misconfigurations
The "atomic test and set of disk block returned false for equality" message is a protective symptom rather than a destructive failure. It proves that your storage architecture's safety guardrails are actively preventing data overwrites. By auditing cluster performance, upgrading system firmware, and optimizing the scheduling of metadata-heavy operations, you can minimize lock contention and restore seamless high-speed performance to your storage infrastructure. In a highly dynamic cluster, multiple hosts frequently
If the block on the disk has changed since the host last checked it, the equality test returns false . The array then returns an "ATS Miscompare" error . Common Causes of This Error Host B’s "Test" phase fails because the disk
When a system displays the error message it indicates that a low-level synchronization command failed because the storage state changed unexpectedly. This mechanism is critical for maintaining a single source of truth across shared infrastructure. The Underlying Technology: VAAI and ATS It proves that your storage architecture's safety guardrails
To understand the error, we must first break down the three core concepts:
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To understand why this error occurs, it is essential to understand how ESXi communicates with shared storage. In a clustered environment, multiple ESXi hosts simultaneously access the same physical storage LUN (Logical Unit Number). To prevent different hosts from overwriting the same metadata block at the same time, a locking mechanism is mandatory.
