Atomic Test And Set Of Disk Block Returned False For Equality __full__ -

If this fails, the problem is at the hardware or SCSI target level.

The SCSI command COMPARE AND WRITE (opcode 0x89) is the hardware-level manifestation of "atomic test and set." Its behavior:

The host reads a specific block of metadata and checks if its current on-disk value matches an expected value known by the host.

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This exposes a tragic tension at the heart of computing: the desire for immutability versus the necessity of mutation. We want data to persist (immutability), but we need to update it (mutation). The test-and-set is the mechanism that brokers this tension. When it returns false, it is a victory for the evolution of the system over the stagnation of the stale view. It prioritizes the "new" truth over the "old" expectation. If this fails, the problem is at the

The "false for equality" part means the data currently on the disk is different from the data the host expected to find. Why This Happens

This isn't just a log entry you can ignore. When an ATS miscompare happens, the ESXi host often loses trust in its connection to the storage. This can trigger: SCSI Resets

The Hidden Ghost in Your SAN: Understanding "Atomic Test and Set Returned False"

If you have encountered this error, you are likely dealing with a race condition, a failing distributed lock, or a corrupted storage volume. This article dissects the error message piece by piece, explains the underlying mechanics of atomic operations on disk blocks, and provides a comprehensive guide to diagnosing and fixing the issue. Share public link This exposes a tragic tension

The "Atomic test and set of disk block returned false for equality" error is a protective mechanism. It prevents a host from overwriting metadata that has changed without its knowledge, avoiding catastrophic volume corruption.

One driver assumes 512-byte blocks; another uses 4096-byte blocks (4K native). Result: Test-and-set on overlapping block regions fails repeatedly. Solution: Standardize block size across all access paths (use blockdev --getbsz and --setbsz ).

: If another host has modified that same block, or if extreme latency caused a previous update to be delayed/retried, the "test" part of the command fails because the current disk image differs from the host's in-memory image.

A VM may briefly stun or become unresponsive if it is waiting on a metadata operation (like expanding a thin-provisioned disk) that is blocked by ATS failures. When it returns false, it is a victory

Elias reached for the physical kill-switch, but the terminal flickered one last message before the screen went black:

To solve this, the T10 standard committee introduced , which VMware implemented as part of vSphere Storage APIs for Array Integration (VAAI) . How ATS Works

To maximize storage efficiency, modern datacenters connect multiple physical servers (hosts) to a centralized storage array. When these hosts write data to the same shared volume simultaneously, they must use a mechanism to prevent overwriting each other's data. The Role of Atomic Test-and-Set (ATS)

Atomic test and set of disk block returned false for equality