Atomic Test And Set Of Disk Block Returned False For Equality
[ Host A ] [ Host B ] | | 1. Reads Block X | | | | 2. Writes Block X | (Changes Data) | | 3. Attempts ATS Write | (Expected != Current) | v | Error: False for Equality | 1. Split-Brain and Multi-Host Contention
Ensure that your storage controllers are running the latest stable microcode provided by the vendor. Manufacturers frequently release patches that optimize how internal cache algorithms process atomic disk primitives under heavy parallel load. Optimize Network Paths and Multipathing Policies
a critical indicator of a metadata mismatch or locking failure in VMware vSphere environments . It typically occurs during an Atomic Test and Set (ATS)
This error message typically appears in logs (such as vmkernel.log ) and indicates a failure in the Atomic Test and Set (ATS) locking mechanism , which is part of the vSphere Storage APIs for Array Integration (VAAI). What it Means [ Host A ] [ Host B ] | | 1
The technical reality of a failed test-and-set often leads to the generation of "garbage." In locking protocols, if a thread attempts to modify a resource without successfully acquiring the lock, the resulting data is often inconsistent, corrupted, or discarded. The "false" is the trigger that prevents this garbage from becoming the dominant reality. It saves the system from a descent into chaos.
The operation happens as a single, uninterruptible unit. No other process can intervene halfway through.
The "Atomic test and set of disk block returned false for equality" error in VMware vSphere indicates a failure in Hardware Assisted Locking (ATS) due to outdated storage metadata, usually caused by concurrency conflicts or high latency. This failure occurs when an ESXi host attempts to update a storage block that has already been modified by another host, requiring investigation into firmware compatibility or disabling ATS heartbeats. For a detailed technical breakdown of this specific issue, review the discussion at Reddit . Attempts ATS Write | (Expected
Update storage controller microcode to resolve known ATS processing bugs.
“atomic test and set of disk block returned false for equality”
In a healthy cluster, when one host holds a lock on a metadata block, other hosts will "spin" or retry their ATS operation until the lock is released. However, if a host is slow to respond or if there's a network glitch, two hosts might believe they are the lock holders. This can cause one host's ATS to fail because the block's data has already been changed by another. Optimize Network Paths and Multipathing Policies a critical
The error message "atomic test and set of disk block returned false for equality"
Resolving persistent ATS equality failures requires a systematic investigation across your virtualization and storage layers. Step 1: Analyze VMkernel Logs
Understanding the "Atomic Test and Set of Disk Block Returned False for Equality" Error
The most poignant part of the prompt is the specific phrasing: "returned false for equality." In the context of a test-and-set, the "equality" in question is the match between the expected state (free/zero) and the actual state found.
This error is most frequently seen in the following scenarios: