nvme-atomic-write-unit-normal · shipping · also AWUN, NAWUN, Namespace Atomic Write Unit Normal

NVMe Atomic Write Unit Normal

Atomic Write Unit Normal is an NVMe controller parameter describing the write size covered by its normal-operation atomicity guarantee relative to other reads and writes.

Related Observatory article: NVMe Atomic Write Unit Normal on hesela.com

AWUN does not describe power-failure protection; AWUPF is the separate interrupted-write parameter. The Write Atomicity Normal feature can disable normal atomicity without disabling power-fail atomicity. [1]

AWUN stores a logical-block count minus one. When NSFEAT bit 1 reports support for namespace atomic parameters, nonzero NAWUN overrides it; NAWUN zero inherits AWUN rather than describing one block. Without that support bit, use the controller field. Convert to bytes using the selected namespace LBA format. [2] [1]

Namespace guarantees also depend on atomic boundaries and the selected atomicity mode. The controller's AWUN baseline must remain supported across namespace boundaries. These device parameters do not by themselves establish Linux file-level support, persistent completion or multi-command transaction atomicity. [1]

Relations

related

NVMe Atomic Write Unit Power Fail, NVMe atomic boundary, NVMe namespace, Torn write, RWF_ATOMIC

Limitations

• Normal-operation atomicity is not power-failure protection or a durable application commit. [1]

Citations

1. NVM Express NVM Command Set 1.3 (2026): sections 2.1.4, 3.3.6 and 4.1.3.4; Figures 123 and 126. Copyright 2008-2026 NVM Express, Inc. All rights reserved. (accessed 2026-11-10)
2. Microsoft: NVME_IDENTIFY_NAMESPACE_DATA, namespace atomic unit and boundary encodings (accessed 2026-11-10)

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