Atomic Test And Set Of Disk Block Returned False For Equality Info

The storage array checks if the actual block data matches the host's expected data. Result:

Atomic Test and Set (ATS) is a hardware-assisted locking method used by ESXi to manage metadata updates on shared storage (VMFS datastores). WordPress.com Traditional Method

In vSphere, this can be done by changing the advanced setting: UserVars.VMFS3HardwareAcceleratedLocking to 0 (Disabled).

You may have computed the expected value incorrectly—for example, using a stale version number. Recompute the expected value by re-reading the block immediately before TAS, not relying on cached data more than a few milliseconds old. The storage array checks if the actual block

When an ATS operation returns "false for equality," it means a mismatch occurred. This mismatch is rarely caused by a failing hard drive; it is almost always an orchestration or communication fault. 1. Multi-Host Contention and Race Conditions

In the world of distributed systems, high-availability clusters, and storage area networks (SANs), data integrity is the highest priority. One of the most cryptic yet significant errors a systems administrator or storage engineer might encounter is:

In VMware environments, the feature uses atomic test-and-set commands (ATS). If the underlying storage array has a firmware bug or a momentary timeout, the ATS primitive may return a false equality, leading to VM freezes or "Lost access to volume" messages. 3. Latency and Connectivity Spikes You may have computed the expected value incorrectly—for

The most frequent cause is excessive metadata activity on a single volume. If dozens of virtual machines on different hosts are booting up, taking snapshots, or migrating via vMotion simultaneously on the same datastore, multiple hosts will compete for the same metadata blocks. One host will win the lock, causing the others to trigger an ATS equality failure. 2. Storage Array Firmware Bugs

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The technical reality of a failed test-and-set often leads to the generation of "garbage." In locking protocols, if a thread attempts to modify a resource without successfully acquiring the lock, the resulting data is often inconsistent, corrupted, or discarded. The "false" is the trigger that prevents this garbage from becoming the dominant reality. It saves the system from a descent into chaos. This mismatch is rarely caused by a failing

The host sends a command to the storage array containing the expected current state of a specific disk block.

Caution: Only clear reservations if you are certain no active node holds them.

The most common scenario leading to this error is a . This occurs primarily during the heartbeat process, where an ESXi host periodically updates its "heartbeat" region on the VMFS volume to signal that it is still alive and maintaining its locks. When an ATS operation on a heartbeat slot fails with "false for equality," the ESXi host loses confidence in its lock on the datastore. This can trigger a series of events, including aborting all outstanding I/O to the datastore and resetting the SCSI device, leading to temporary connectivity loss and application disruptions.

The entire process happens at the hardware level in a single, uninterrupted (atomic) step. Decoding the Error Message