: Under extreme latency, an ATS command might time out. The host assumes the write failed and tries again using the old "test" image. However, if the first write actually made it to the disk just before being aborted, the second attempt will fail because the disk has already changed. High Concurrency Overload
Note: Disabling ATS completely is highly discouraged in modern setups as it drastically reduces storage performance. Always consult your storage vendor's compatibility matrix before changing advanced advanced storage parameters. Conclusion
The operation happens as a single, uninterruptible unit. No other process can intervene halfway through.
If you encounter this error, follow these steps to resolve it, ensuring you have the latest Broadcom/VMware knowledge base access: A. Immediate Mitigation (Get Hosts Running) : Under extreme latency, an ATS command might time out
On Linux with SCSI devices:
Check for physical link errors (e.g., CRC errors on Fibre Channel switches) that could cause ATS command timeouts. Step 4: Fall Back to ATS+SCSI Locking (If Necessary)
"atomic test and set of disk block returned false for equality" High Concurrency Overload Note: Disabling ATS completely is
Instead of locking the whole LUN, ATS allows a host to lock a specific sector or disk block. The operation is atomic, meaning it happens completely or not at all, using a two-step verification process:
: In some cases, vendors (like NetApp or Pure Storage) recommend disabling ATS for heartbeating if the storage array does not support it correctly under specific conditions.
When applying Atomic Test-and-Set to a "disk block," the scenario typically falls into one of two architectural patterns: No other process can intervene halfway through
The error message is a critical alert generated within enterprise storage environments—most notably inside VMware ESXi ( vmkernel.log ) kernels. It signals a failure in Hardware Assisted Locking (VAAI ATS) , meaning that an ESXi host attempted to lock or update a specific disk block on a shared datastore, but the underlying storage array rejected the operation because the expected disk state did not match reality .
When the operation returns "false," it is not merely reporting that the block was locked. It is reporting a collision in the timeline of the machine. It signifies that in the microscopic gap between the intention to act and the execution of the act, the universe changed. Another process, perhaps running on a core a fraction of a millisecond faster, or a network packet arriving from a continent away, touched that block first. The "false" is the system acknowledging that the operator was too late. It is the digital equivalent of reaching out to shake a hand only to find the other person has already turned away.
By understanding the atomic semantics of modern disk interfaces, from SCSI Compare-and-Write to NVMe’s atomic operations, you can transform this cryptic error from a headache into a useful diagnostic signal. Implement robust retry logic, monitor your persistent reservations, and always validate block integrity.
When this error begins spamming your logs, it cascades into several disruptive infrastructural behaviors:
: Incompatibilities between specific storage array firmwares and ESXi (particularly ESXi 6.5 and VMFS6) have historically triggered these errors. The Impact: Why You Should Care