Atomic Test And Set Of Disk Block Returned False For Equality

Ensure your storage array fully supports and correctly implements hardware-assisted locking. For example, on VMware ESXi hosts, you can check if ATS is enabled globally using the CLI:

sg_inq /dev/sdX sg_persist -i /dev/sdX # Show all registered initiators

CRITICAL: ATOMIC TEST AND SET OF DISK BLOCK RETURNED FALSE FOR EQUALITY.

The hostd and vpxa management services on the ESXi host can fall into a degraded state, causing the host to show as "Not Responding" in vCenter.

When this error appears in your VMkernel logs, it points to one of three underlying system failures: 1. High I/O Latency and Storage Array Overload Ensure your storage array fully supports and correctly

esxcli system settings advanced list -o /VMFS3/HardwareAcceleratedLocking Use code with caution.

Indicates a localized pathing, workload, or configuration issue on that specific Datastore.

Check kernel logs ( dmesg ), system logs ( /var/log/messages ), and application logs:

Storage arrays handle the hardware execution of the COMPARE AND WRITE command. Bugs in the array's microcode or firmware can cause it to misinterpret the block data, fail to process the atomic transaction fast enough, or falsely report a mismatch. 3. Network Latency and Packet Loss When this error appears in your VMkernel logs,

Historically, hosts used standard SCSI reservations ( Reserve and Release commands). This mechanism locked the entire LUN . While one host updated a tiny fraction of metadata, all other hosts were blocked from sending I/O to that LUN, creating major performance bottlenecks in large clusters.

If a node crashes unexpectedly, it may leave a stale lock on a specific disk block. When a surviving node attempts to acquire or modify that block using an ATS instruction, the existing lock metadata causes the equality check to fail. How to Diagnose and Troubleshoot

Fixing this error requires isolating whether the fault lies in host clustering, fabric communication, or storage array firmware. Step 1: Identify the Affected Volume and Hosts

To help isolate your specific issue, please share a few more details: Check kernel logs ( dmesg ), system logs

When this error begins spamming your logs, it cascades into several disruptive infrastructural behaviors:

This breakdown helps to illuminate where the error originates.

During an ATS operation, the ESXi host issues a COMPARE AND WRITE command. It sends two images to the storage array: a (what it believes is currently written on the disk) and a "Set" image (the modification it wants to write). The storage array evaluates this atomically:

operation, where an ESXi host attempts to update a datastore's heartbeat or lock a file but finds that the data on the disk does not match what it expected. Core Cause: ATS Miscompare Heartbeat Mechanism