If the system finds "State C" instead, the equality test fails. The operation returns false , and the write is aborted to prevent overwriting someone else's data. 🔍 Common Causes for the Equality Failure
VAAI is a set of storage primitives that offload specific tasks from the ESXi host to the storage array, improving performance and scalability. One of these primitives is ATS , also known as "Hardware Assisted Locking". Before ATS , VMFS used SCSI-2 reservations, which locked an entire LUN (Logical Unit Number), preventing any other host from accessing it, even for unrelated operations. ATS solves this by allowing fine-grained, block-level locking. Instead of locking the whole LUN, a host can lock only the specific disk block it needs to update. This significantly reduces lock contention in shared-storage environments.
If the error persists on a single datastore while others are fine, the VMFS volume might have metadata corruption requiring technical support intervention. Conclusion If the system finds "State C" instead, the
Mixing drives with different sector sizes (such as native 4Kn drives and 512-byte emulation/512e drives) in the same storage pool can cause misalignment. When the host expects a specific block boundary for an ATS operation and encounters a mismatch, it returns an equality failure. Symptoms and Impact on the Environment
while (atomic_test_and_set(disk_block, expected, new) == false) // Another node won the race current_leader = read_leader_from_disk(); if (current_leader == myself) // Possibly stale cache, re-read block invalidate_disk_cache(); else backoff_and_retry(); One of these primitives is ATS , also
user wants a detailed article on "atomic test and set of disk block returned false for equality". This keyword seems technical, likely related to concurrency control in operating systems or database systems, specifically the "test-and-set" atomic operation on disk blocks. I need to search for relevant information. I'll break down the search into multiple queries to cover different aspects. search results show some relevant information. Result 1 from search 2 seems to be a VMware community thread about the exact error message. Result 0 from search 2 is about Synology NAS iSCSI ATS reliability issues. Result 2 from search 2 is a VMware community thread. These could be useful. I'll open them. search results also show something about "tests: Fix expected value after test_and_set atomic op". That might be relevant. I'll open it. the link is not accessible. I'll search for "test_and_set atomic op expected value".'ll open result 1. search for "VMware ATS miscompare". 0 from search 13 seems to be a VMware KB article. I'll open it. result 1 from search 13 might be relevant. I'll open it. result 5 from search 13., I recall that "test-and-set" is a CPU instruction for mutual exclusion. The keyword might refer to a specific error in VMware ESXi when using VAAI ATS (Atomic Test and Set) operations. The error "Atomic test and set of disk block returned false for equality" appears in VMware logs. I should explain this error in the context of VMware vSphere, VAAI, and ATS locking. I'll search for more details.'ll open result 1. result 2 from search 17.'ll open the specific post about ATS miscompare.'ll open result 1.'ll continue reading.'ll also open result 2 from search 20.'ll also search for "VMFS ATS heartbeat". I have a good understanding of the keyword. It's an error message in VMware ESXi when an ATS operation fails. I'll structure the article as follows: introduction, understanding the basics (atomic operations, test-and-set, disk blocks), ATS in VMware VAAI, the error "returned false for equality", common scenarios and root causes, troubleshooting, solutions, and conclusion.
I can provide specific configuration commands or vendor-specific workarounds based on your setup. Share public link Instead of locking the whole LUN, a host
Severe delays in storage communication can cause the host to time out or see outdated metadata.
Historically, hosts used SCSI reservations ( SCSI-2 Reservation ), which locked the entire LUN. This caused massive performance degradation because other hosts had to wait for the entire volume to unlock just to modify a single file.