nvme-atomic-write-unit-power-fail · shipping · also AWUPF, NAWUPF, Namespace Atomic Write Unit Power Fail

NVMe Atomic Write Unit Power Fail

Atomic Write Unit Power Fail is an NVMe controller parameter describing the write size covered by its atomicity guarantee when power loss or another error interrupts a write.

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

Within the applicable size, boundary and mode conditions, an interrupted write does not leave a mixture of old and new logical blocks in its atomic range. This is distinct from normal-operation atomicity, described by AWUN. [1]

AWUPF stores a logical-block count minus one. If namespace atomic parameters are supported, nonzero NAWUPF overrides it; NAWUPF zero inherits AWUPF. Namespace parameters may change when the LBA format changes. [2] [1]

Atomicity alone does not establish persistence of the new value. Section 2.1.4.3.2 describes conditions where acknowledged data still in volatile cache may be lost after power failure. Write FUA requires its data and metadata to reach nonvolatile media before completion, without ordering other commands. [1]

The controller AWUPF baseline remains valid across namespace boundaries; larger namespace guarantees have additional boundary conditions. Multiple Atomicity Mode protects individual subranges, not the whole spanning command as one transaction. [1]

Relations

related

NVMe Atomic Write Unit Normal, NVMe atomic boundary, NVMe namespace, Torn write, Force Unit Access, Storage cache flush

Limitations

• An atomic recovery range does not establish durable completion or an atomic multi-command transaction. [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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