Ensure your HBA (Host Bus Adapter) drivers and the storage array firmware are on the vendor's "Compatibility Matrix."

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

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

If the host cannot "set" the lock, it cannot write to the disk.

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