Atomic Test And Set Of Disk Block Returned False For Equality __full__ May 2026

The message "Atomic test and set of disk block returned false for equality" is a critical diagnostic error typically associated with VMware ESXi and storage systems using VAAI (vSphere Storage APIs – Array Integration).

Concurrency Conflicts: If another host successfully updated the block metadata just milliseconds before, the original host's "expected" data is now stale, triggering the miscompare.

: VMFS inode inconsistency or corruption in the catalog directory, specifically related to file mechanisms, can prevent successful ATS locks. Driver/Firmware Bugs : Outdated or buggy HBA (Host Bus Adapter) The message "Atomic test and set of disk

“Atomic compare-and-swap on disk block failed: equality check returned false. Expected value did not match actual block content. Possible causes: concurrent write by another process, or cached expected value outdated.”

: You may see vCenter alarms stating "Path redundancy to storage degraded". Host Hangs : In severe cases, the Driver/Firmware Bugs : Outdated or buggy HBA (Host

The returned false value for equality may lead to:

TEST FAILED. SUBJECT ELIAS DETECTED. SETTING EQUALITY TO ZERO. Host Hangs : In severe cases, the The

“The atomic test-and-set operation on the disk block returned false when checking for equality, indicating that the current value in the block did not match the expected value. This suggests a concurrent modification or a stale expected value — the operation failed as designed, preventing a potential race condition or lost update.”

The Checklist: