NVME-COMPARE(1)

✨ NVME-COMPARE ✨

okay bestie, buckle up — this is the nvme-compare page from the NVMe Manual and it's literally the tool that goes "wait, is this what I think it is?" at your drive 🔥

💖 NAME 💖

nvme-compare — send an NVMe Compare command, and get the results back, no cap.

🦋 SYNOPSIS 🦋

nvme [<global-options>] compare <device>
                        [--start-block=<slba> | -s <slba>]
                        [--block-count=<nlb> | -c <nlb>]
                        [--block-size=<size> | -b <size>]
                        [--data-size=<size> | -z <size>]
                        [--metadata-size=<metasize> | -y <metasize>]
                        [--ref-tag=<reftag> | -r <reftag>]
                        [--data=<data-file> | -d <data-file>]
                        [--metadata=<meta> | -M <meta>]
                        [--prinfo=<prinfo> | -p <prinfo>]
                        [--app-tag-mask=<appmask> | -m <appmask>]
                        [--app-tag=<apptag> | -a <apptag>]
                        [--limited-retry | -l]
                        [--force-unit-access | -f]
                        [--dir-type=<type> | -T <type>]
                        [--dir-spec=<spec> | -S <spec>]
                        [--dsm=<dsm> | -D <dsm>]
                        [--show-command | -V]
                        [--dry-run | -w]
                        [--latency | -t]
                        [--storage-tag<storage-tag> | -g <storage-tag>]
                        [--storage-tag-check | -C]
                        [--force]

like, yes, that's a lot of flags, but we're gonna get through them together 🫶

🌸 DESCRIPTION 🌸

okay so picture this: the Compare command reads the logical blocks that the command specifies from the medium, and then it compares the data it just read against a comparison data buffer that got transferred along as part of the command. it's giving vibe check for your blocks 💅

if the data read from the controller and the comparison data buffer are equivalent with no miscompares, then the command completes successfully. slay. 🎀

but if there is any miscompare, the command completes with an error of Compare Failure — so like, it's not the same, and the drive is telling you that. 😭

and if metadata is provided, then a comparison is also performed for the metadata. periodt.

🎀 OPTIONS 🎀

• -s <slba>, --start-block=<slba> — 64-bit address of the first block to access.
• -c <nlb>, --block-count=<nlb> — number of blocks to be accessed (zero-based, bestie, zero-based).
• -b <size>, --block-size=<size> — if you specify it, this is the logical block size in bytes, with metasize also describing the metadata size for an individual block. otherwise it gets discovered by identify namespace. iykyk ✨
• -z <size>, --data-size=<size> — size of data to be compared, in bytes.
• -y <metasize>, --metadata-size=<metasize> — size of metadata to be transferred, in bytes.
• -r <reftag>, --ref-tag=<reftag> — Reference Tag for Protection Information.
• -d <data-file>, --data=<data-file> — Data file.
• -M <meta>, --metadata=<meta> — Metadata file.
• -p <prinfo>, --prinfo=<prinfo> — Protection Information and check field. okay here's the breakdown, bc this one's a whole mood:
  • Bit 3 — PRACT: Protection Information Action. when set to 1, PI is stripped/inserted on read/write when the block format's metadata size is 8. when set to 0, metadata is passes.
  • Bits 2:0 — PRCHK: Protection Information Check:
    • Bit 2 — set to 1 enables checking the guard tag.
    • Bit 1 — set to 1 enables checking the application tag.
    • Bit 0 — set to 1 enables checking the reference tag.
• -m <appmask>, --app-tag-mask=<appmask> — App Tag Mask for Protection Information.
• -a <apptag>, --app-tag=<apptag> — App Tag for Protection Information.
• -l, --limited-retry — Number of limited attempts to media.
• -f, --force-unit-access — FUA option to guarantee that data is stored to media.
• -T <type>, --dir-type=<type> — optional directive type. heads up: the nvme-cli only enforces that the value be in the defined range for the directive type, though the NVMe specification (1.3a) defines only one directive, 01h, for write stream identifiers.
• -S <spec>, --dir-spec=<spec> — optional field for directive specifics. when used with write streams, this value is defined to be the write stream identifier. and ngl, the nvme-cli will not validate that the stream requested is within the controller's capabilities. 🙈
• -D <dsm>, --dsm=<dsm> — the optional data set management attributes for this command. the argument for this is the least significant 8 bits of the DSM field in a write command; the most significant 16 bits of the field come from the directive specific field, if used. you can use this to set attributes for the LBAs being written — like access frequency, type, latency, among other things — as well as yet to be defined types. please consult the NVMe specification for a detailed breakdown of how to use this field.
• -V, --show-cmd — print out the command to be sent.
• -w, --dry-run — do not actually send the command. but bestie listen: if you want to use --dry-run, the --show-cmd option must be set. otherwise --dry-run will be ignored. 💀
• -t, --latency — print out the latency the IOCTL took (in us).
• -g <storage-tag>, --storage-tag=<storage-tag> — Variable Sized Expected Logical Block Storage Tag (ELBST).
• -C, --storage-tag-check — this flag enables Storage Tag field checking as part of end-to-end data protection processing.
• --force — ignore that the namespace is currently busy and performs the operation even though. 😭 (yes, it just... does it anyway)

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🌈 GLOBAL OPTIONS 🌈

these ones live at the top-level nvme command, and they're available to this subcommand too — so they're not just for compare, but they're absolutely invited to the party 🫶

• --dry-run — print the command that would be executed, but do not actually execute it.
• --no-ioctl-probing — disable probing for 64-bit IOCTL support.
• --no-retries — disable retry logic on transient errors.
• -o <fmt>, --output-format=<fmt> — set the reporting format to normal, tabular, 'json, or binary. only one output format may be used at a time.
• --output-format-version=<version> — select the output format version. version 1 uses the original field naming, while version 2 (default) provides more consistent and script-friendly field names. other versions are rejected. 🚫
• --quiet — suppress informational messages. errors are still reported, and --quiet cancels any --verbose for the library log level.
• --set-options=<key=value>[,<key=value>...] — set libnvme library options for this invocation. the supported keys are force-4k, mi-probe-enabled, test-base-dir and test-sysfs-dir.
• --timeout=<ms> — set the timeout for the command in milliseconds. infinite or -1 waits without a time limit (0xffffffff). iconic ⭐
• -v, --verbose — increase the level of detail in the output. may be specified multiple times to further increase verbosity. spam it, queen 👑

also these options can be set as machine-wide defaults in nvme-cli.conf(5) — and a command-line flag always overrides the file. always. no exceptions. 💅

🍓 EXAMPLES 🍓

No examples yet.

(i know. tragic. the docs are still getting ready, give her time 🧚)

👑 NVME 👑

Part of the nvme-user suite. main character energy, honestly.

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and that's the whole page, bestie — written by the NVMe crew, dated 10/30/2026, and you made it all the way to the bottom which means you ate and left no crumbs 💖✨🎀