Atomic Test And Set Of Disk Block Returned False For Equality !!link!! Jun 2026

If you work with distributed databases (like Cassandra, ScyllaDB, or FoundationDB), Ceph, or any system that uses complex consensus algorithms (Raft/Paxos), you might eventually stumble upon a terrifying log message:

Drop a comment below with your hardware specs. I’ll bet it was an NVMe drive from 2018. If you work with distributed databases (like Cassandra,

In some specific storage environments (notably certain older NAS or SAN setups), the ATS heartbeating mechanism is too aggressive. VMware allows you to revert to traditional SCSI reservations for heartbeating while keeping ATS for other tasks, though this should only be done under the guidance of support. VMware allows you to revert to traditional SCSI

The error message explicitly tells you: false for equality means the atomic compare-and-swap (CAS) operation failed because the value on disk was not equal to the expected value. What is Atomic Test and Set (ATS)

, a technical standoff between your ESXi host and your storage array that can lead to datastore disconnects, VM crashes, and major performance degradations. What is Atomic Test and Set (ATS)?

The host reads a block and compares it to a "test-image" (expected data) .