Atomic Test And Set Of Disk Block Returned False For Equality ((full)) Direct

"Atomic test and set of disk block returned false for equality" is a low-level status message typically found in VMware ESXi VMkernel logs It indicates a failure in the Atomic Test and Set (ATS) , which is part of the vStorage APIs for Array Integration (VAAI) Core Concept: What is ATS?

do expected = read_disk_block(block_id); new_value = expected + 1; while (!atomic_test_and_set(block_id, expected, new_value));

In computing, an is a "do-it-all-at-once" operation. It looks at a value, checks if it matches what it expects, and—if it does—updates it instantly. This prevents two different processes from accidentally grabbing the same resource at the exact same time. When it returns false for equality , it means: "Atomic test and set of disk block returned

The Ghost in the Machine: Debugging "Atomic Test-and-Set of Disk Block Returned False for Equality"

The message is a critical diagnostic error typically associated with VMware ESXi and storage systems using VAAI (vSphere Storage APIs – Array Integration) . 10-node Ceph cluster, BlueStore backend, NVMe-over-Fabrics

: If you are seeing "Lost access to datastore" messages alongside this error, VMware often recommends disabling ATS for heartbeating (switching back to legacy SCSI reservations) as a workaround on affected arrays.

10-node Ceph cluster, BlueStore backend, NVMe-over-Fabrics. Error: OSD logs repeated: bluestore/StupidAllocator.cc: atomic test and set of disk block 0x4a20b returned false for equality . Root cause: A network partition caused two OSDs to believe they held the same allocation bitmap lock. The storage array (NVMe target) correctly rejected the second OSD’s compare-and-write. Fix: Reduced osd_heartbeat_grace from 20s to 5s, enabled faster fencing, and implemented retry logic with jitter. enabled faster fencing

: The storage array compares the actual data on the disk with the host's provided data.