When you encounter the "atomic test and set of disk block returned false for equality" error, a structured approach is necessary to identify and fix the underlying problem.
While alarming, the error is usually resolvable. The key is methodical troubleshooting: start by verifying the health and capacity of the storage array, then check for configuration issues or resource exhaustion. In many cases, particularly with legacy setups or problematic arrays, the workaround of disabling ATS for the VMFS heartbeat is an effective solution.
The error message, "Atomic test and set of disk block returned false for equality," is an indicator that this fundamental locking mechanism has encountered a problem. While the exact message may appear in various contexts, it is most famously associated with VMware’s vSphere hypervisor when using the VMFS (Virtual Machine File System). Let's break down the components of this error to understand what it means. When you encounter the "atomic test and set
When the system reports that this operation "returned false for equality," it means the phase failed.
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 In many cases, particularly with legacy setups or
The "atomic test and set of disk block returned false for equality" error is a protective measure. While it causes disruptive downtime, it exists to prevent the "silent killer" of enterprise computing: By failing the operation when the state doesn't match, the system ensures that two hosts never write to the same block simultaneously, preserving the integrity of your databases and virtual machines.
sg_compare_and_write --read-blk=0 --verify-blk=0 --write-blk=0 --in=NEWDATA.bin /dev/sdX Let's break down the components of this error
ATS is a storage hardware acceleration feature (part of VAAI) used by ESXi to lock individual disk blocks rather than an entire LUN.
I'll search for more details on VAAI ATS. search for "SCSI opcode 0x89 compare and write".'ll open result 0.'ll also search for "test_and_set_bit_lock". have reached the maximum number of steps. I need to formulate an answer based on the information gathered so far. The user wants a long article about the keyword "atomic test and set of disk block returned false for equality". I have collected relevant information, particularly regarding VMware ESXi and ATS miscompare errors. I will structure the article to first explain the foundational concepts of atomic operations and test-and-set, then delve into the specifics of the error message in the context of VMware's VAAI ATS, discuss the root causes, provide troubleshooting steps, and conclude with best practices. I will cite the sources I have found, such as the VMware community threads, KB articles, and Cormac Hogan's blog posts. Now I will write the article. article provides an in-depth look at the "atomic test and set of disk block returned false for equality" error. We will explore what an atomic test and set (ATS) operation is, how it applies to storage systems, and why this specific error occurs, particularly in VMware vSphere environments. By the end, you will understand the technical background and have practical guidance for diagnosing and resolving the issue.
The operation happens as a single, uninterruptible unit. No other process can intervene halfway through.