NVM Command Set 1.3: Logical blocks, I/O commands, and data protection

01 Namespace capacity and allocation

01.01.Separate logical address space from allocated resources before considering writes and deallocation. Returned data and allocation state answer different questions.

NCAP

Namespace Capacity, the maximum number of simultaneously allocated logical blocks.

NSZE

Namespace Size, the total number of addressable logical blocks.

NUSE

Namespace Utilization, the number of currently allocated logical blocks.

01.02.NSZE ≥ NCAP ≥ NUSE: NSZE defines the addressable range, NCAP limits simultaneously allocated blocks, and NUSE counts current allocation. THINP=0 requires NCAP=NSZE. NVMCAP is measured in bytes and is not necessarily NSZE multiplied by data size.

NVMCAP

NVM Capacity, measured in bytes; not directly comparable to NSZE/NCAP logical-block counts.

THINP

Thin Provisioning, the NSFEAT bit governing whether NCAP may be below NSZE and whether the controller tracks NUSE.

02 Metadata transfer and PI placement

02.01.Metadata need not consist entirely of PI. Mark data, non-PI metadata, and PI separately before computing host-buffer size and CRC coverage.

CRC

Cyclic Redundancy Check: a check value computed from data bits to detect changes.

PI

Protection Information: Guard and tag fields used to check data and its associated information.

DPTR

Command data pointer: destination for Read, source for Write, descriptors for Copy/DSM.

MPTR

Separate-metadata pointer; namespace format and command fields determine metadata placement.

02.02.Formatting selects one metadata transfer mechanism per namespace: contiguous extended LBAs or a separate buffer addressed by MPTR. Metadata cannot be split between the mechanisms and must be written atomically with its associated logical block.

logical block

An addressable unit in a namespace; its data size is determined by the active format.

PRP

Physical Region Page, a pointer format describing a host-addressable data buffer in memory-page units.

SGL

Scatter Gather List, a descriptor-and-segment format for one or more data-buffer regions.

03 Read/Write data and completion

03.01.Check range, buffer, PI, and completion separately to distinguish addressing errors, format mismatches, and media failures.

03.02.Read/Write specify a contiguous range with SLBA and zero-based NLB. DPTR is a destination buffer for Read and a source buffer for Write. FUA=1 requires nonvolatile-media handling without implying ordering of other commands.

zero-based

zero-based: numbering starts at zero, so raw=3 can mean the fourth item or four units; the field definition still decides which.

SLBA

Starting LBA; Starts the command range.

FUA

Force Unit Access; requires nonvolatile-media semantics without automatically ordering other commands.

NLB

Number of Logical Blocks; this field in the report’s commands/status descriptors is zero-based. DSM LLB is separately one-based.

CETYPE

Command Extension Type; Selects the interpretation of the command extension value CEV.

PRINFO

Protection Information; The command field combining PRACT and PRCHK.

DSPEC

Directive Specific; Its contents depend on the Directive type.

DTYPE

Directive Type; Selects the Directive type for the command.

CDW

CDW (Command Dword): a 32-bit command field. In CDW10, 10 is the field index, not a byte offset.

CEV

Command Extension Value; Its contents are interpreted according to CETYPE.

DSM

Dataset Management: host hints about use and allocation of data ranges.

STC

Storage Tag Check, separate from three-bit PRCHK and ignored when STS=0.

LR

Limited Retry; selects retry behavior governed by Error Recovery policy.

04 Normal, power-fail, and multiple atomicity

04.01.Read size, starting alignment, NSABP, and MAM together. Atomicity and persistence on nonvolatile media are separate checks; FUA/Flush do not establish ordering for other commands.

NSABP

Namespace Atomic Boundary Parameters: indicates applicability of namespace atomic-write parameters.

MAM

Multiple Atomicity Mode; a crossing command is divided into independently atomic subranges.

04.02.AWUN/NAWUN and AWUPF/NAWUPF describe normal and failure-condition atomicity. Single Atomicity Mode provides no whole-command guarantee across a boundary; Multiple Atomicity Mode divides the range at boundaries into separately atomic subranges, without promising one combined outcome.

NAWUPF

Namespace Atomic Write Unit Power Fail; Namespace failure-condition atomic-write size, subject to applicability and zero-value rules.

AWUPF

Atomic Write Unit Power Fail, the zero-based atomic size for failure conditions.

NAWUN

Namespace Atomic Write Unit Normal; Namespace normal atomic-write size, subject to applicability and zero-value rules.

AWUN

Atomic Write Unit Normal, the controller’s zero-based normal atomic-write size.

NABSPF

Namespace Atomic Boundary Size Power Fail; The failure-condition atomic boundary size.

offset

offset: a displacement measured from a stated start. It answers “how far from the start,” unlike an index.

NABSN

Namespace Atomic Boundary Size Normal; The normal-operation atomic boundary size.

NABO

Namespace Atomic Boundary Offset; determines the first boundary location.

FID

Feature Identifier: selects the Feature to read or configure.

DN

Disable Normal in Write Atomicity Normal; does not remove power-fail atomicity.

05 Compare and Verify answer different questions

05.01.Expected-content comparison, integrity verification, and ordinary Read provide different evidence. Compare excludes PI from metadata comparison and checks PI separately as requested.

05.02.Compare compares media data with a host-supplied buffer. Verify checks stored-data integrity without returning data or metadata to the host. Both require PRACT=0; Verify and Read need not report an identical error code for a detected failure.

VSL

Verify Size Limit; A Verify size limit, interpreted with its variant capability.

06 Copy: source descriptors, contiguous destination, partial failure

06.01.Calculate the expanded destination range before checking formats, limits, overlap, and atomicity. Copy reduces host data movement but is not an unconditional transaction.

06.02.Copy concatenates one or more source ranges in descriptor order into one contiguous destination range. Formats 0h/1h use one namespace; 2h/3h carry SNSID and require controller support and host enablement. Failure CQE DW0 is the lowest unsuccessful source index; later ranges may already have been copied.

SNSID

Source Namespace Identifier; Selects a Copy source namespace.

index

index: selects an item or format in a list. It answers “which one,” not “how far from the start.”

CQE

Completion Queue Entry, one completion-result structure in a CQ.

DNR

Do Not Retry, a CQE-status bit indicating that retrying the same command is not expected to succeed.

FCO

Fast Copy Only; requests a fast-copy method for the applicable source.

NR

Zero-based range-count field; actual descriptor count is NR+1.

07 Combining PRACT with PRCHK/STC

07.01.First determine whether namespace PI is enabled, then choose a processing branch by command direction and metadata size. Evaluate checking bits and special disable values afterward.

07.02.PRACT controls PI transfer, insertion, stripping, or replacement. PRCHK Guard/Application/Reference bits and independent STC control checking. With PRACT=1 and MS>PI size, Read still returns all metadata; PRACT=1 does not universally mean stripping PI.

Guard

The PI check-value field; the selected format determines its width and calculation.

PRCHK

Protection Information Check bits for Guard, Application, and Reference.

RTCHK

Reference Tag Check; Requests Reference Tag checking.

08 Hard/Soft modes and token-bucket examples

08.01.Interpret results using capability, configured limits, and actual demand. A configured ratio does not force a fixed throughput ratio at every instant; internal resources and workload still matter.

08.02.Hard Limit sets a ceiling; Soft Limit can use unused bandwidth/IOPS. Resource shortfalls are shared proportionally to configured limits. Appendix A illustrates multiple token buckets without requiring one identical controller implementation.

IOPS

Input/Output Operations Per Second; an operation rate, distinct from byte throughput.

WRIOPSR

Write-to-Read IOPS Ratio; The write-to-read operation-count weight.

WRBWR

Write-to-Read Bandwidth Ratio; The write-to-read bandwidth weight.