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

If it matches (equality), the host updates the block with its own signature to claim ownership.

The host may mark the storage as "All Paths Down" (APD) or "Permanent Device Loss" (PDL) to protect data integrity. If it matches (equality), the host updates the

Why would the equality test fail? Usually, it's one of three scenarios: 1. "Split Brain" or Multi-Host Contention Usually, it's one of three scenarios: 1

The most common cause is that two different hosts are trying to access the same metadata at the exact same time. If Host A updates a block while Host B is still holding onto "old" information about that block, Host B’s next ATS command will fail because the block's state changed behind its back. 2. Storage Array Firmware Incompatibilities Network Latency and Heartbeating Issues

To understand the error, we first have to understand the mechanism. is a hardware-offloaded locking mechanism (often part of the VAAI—vSphere Storage APIs for Array Integration—feature set in VMware environments).

Not all storage arrays implement VAAI/ATS the same way. If there is a bug in the array's microcode or if the host's driver is sending a malformed request, the array might reject the ATS heartbeat, leading to "false for equality" errors even if no real contention exists. 3. Network Latency and Heartbeating Issues