In computer science, an atomic "test-and-set" operation is a way to ensure that only one process can access a shared resource at a time. It's a fundamental synchronization primitive.
ATS relies on a bidirectional handshake between the hypervisor and the storage controller. Microcode bugs in the storage array firmware or outdated Host Bus Adapter (HBA) drivers on the ESXi host can cause the array to interpret or process ATS primitives incorrectly, leading to false mismatches. ESXi host HBAs offline - Broadcom support portal
Determine what was happening in your environment when the error occurred. Did it coincide with: A scheduled backup window utilizing storage snapshots? A massive automated VMotion/Live Migration task? Network switch maintenance or firmware upgrades? Step 3: Verify Storage Fabric Health
When you see the error "atomic test and set of disk block returned false for equality" , the array has executed step 3. The host’s cached map of the storage metadata is out of sync with the actual physical reality on the disk array. Common Root Causes In computer science, an atomic "test-and-set" operation is
The miscompare indicates a breakdown in the between cluster nodes. A mismatch typically arises from one of three primary scenarios:
service can enter a degraded state, making the host unresponsive to management commands. How to Fix It
“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 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.” Microcode bugs in the storage array firmware or
Run file system checks to ensure the metadata is not corrupted. # Example for ext4 fsck.ext4 -f /dev/sdx1 Use code with caution. 3. Review Storage Firmware
When applying Atomic Test-and-Set to a "disk block," the scenario typically falls into one of two architectural patterns:
If it matches (equality), the host updates the block with its own signature to claim ownership. A massive automated VMotion/Live Migration task
The error message "atomic test and set of disk block returned false for equality"
The storage array looks at the actual block on the disk. If the current disk data matches the "expected" data provided by the host, the array permits the write operation.
If rebooting is not possible, try unmounting and remounting the datastore to refresh the locks. B. Long-Term Fixes (Prevent Future Occurrences)