init: correct first-run disk space estimate #35948

l0rinc commented at 10:35 PM on August 10, 2026: contributor

Problem: The assumed blockchain size is maintained in GiB, but the first-run disk-space warning labels it as GB. For pruned nodes, the warning also displays the full-chain estimate even though the check uses the lower of the prune target and that estimate. The chainparams API comments likewise describe both assumed sizes as GB.

Fix: Label the warning as GiB, display the same rounded-up GiB estimate that the disk-space check uses, and document both assumed sizes as GiB.

This PR revives the first-run warning fixes from #29678.

DrahtBot commented at 10:35 PM on August 10, 2026: contributor

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35948.

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Type	Reviewers
ACK	murchandamus, jeanpablojp, achow101
Stale ACK	mercie-ux

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mercie-ux commented at 6:28 AM on August 12, 2026: contributor

ACK fc4342822b

Traced the 856 in chainparams.cpp through both the old and new math. Found a real 63 GB gap between what the check silently required and what the GUI ever showed. Confirmed.

DrahtBot added the label Needs rebase on Aug 14, 2026

achow101 commented at 10:36 PM on August 17, 2026: member

Rather than changing the units that we use in the code, why not change the units as displayed to the user? It shouldn't be that hard to change the units in startup messages since those are just strings.

As one of the people who do/review the chainparams updates, I strongly prefer to use GiB rather than GB since du uses the *iB units by default. Most of these updates are done by looking at commands used in previous PRs, none of which have used *iB units, so I would expect this to be a little bit confusing. Also *B units is actually (annoyingly) ambiguous since some places use it to mean multiples of 1024 (i.e. same as *iB) while others use it as multiples of 1000. The *iB units are actually unambiguous.

l0rinc renamed this:
~~init: correct first-run disk space estimates~~
init: correct first-run disk space estimate
on Aug 17, 2026

init: correct first-run disk space estimate

The assumed blockchain size is maintained in GiB, but the first-run warning labels it as GB.
For pruned nodes, the disk-space check uses the lower prune target while the warning displays the full-chain size.

Label the value as GiB and round the checked byte estimate up to GiB so the warning describes the selected storage mode.

Co-authored-by: Luke Dashjr <luke-jr+git@utopios.org>
Co-authored-by: Ava Chow <github@achow101.com>

42215b8581

l0rinc force-pushed on Aug 17, 2026

l0rinc commented at 11:24 PM on August 17, 2026: contributor

I assumed the original change had a good reason for moving these values to GB, but keeping them in GiB makes this change a lot simpler! Thanks for the review, pushed and added you as a co-author.

DrahtBot removed the label Needs rebase on Aug 18, 2026

murchandamus commented at 10:29 PM on August 21, 2026: member

ACK 42215b85811a4950265fa2d02b22e83046ed95d5

Thanks for picking this up. — I’m not sure the co-authorship is needed here, your code is not reusing any of the lines from the original, you’re just proposing an alternative fix to the identified problem.

jeanpablojp commented at 10:13 PM on August 22, 2026: contributor

tACK 42215b85811a4950265fa2d02b22e83046ed95d5

Ran the pruned case on a 585 MiB volume, -prune=550 makes master warn about 856 GB where this branch says 1 GiB.

fanquake commented at 9:15 AM on August 24, 2026: member

cc @hebasto @GBKS given comments in #29678.

achow101 commented at 9:22 PM on August 24, 2026: member

ACK 42215b85811a4950265fa2d02b22e83046ed95d5

Going to wait for a UI person's opinion before merging though.

fanquake commented at 10:53 PM on August 24, 2026: member

before merging though.

Given this was changed to change strings, and we past string/translation freeze, I don't think it can be merged anyways?

achow101 commented at 11:09 PM on August 24, 2026: member

Given this was changed to change strings, and we past string/translation freeze

oh right

maflcko added this to the milestone 33.0 on Aug 25, 2026

in src/init.cpp:2016 in 42215b8581

2009 | @@ -2009,10 +2010,10 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
2010 |          if (!CheckDiskSpace(args.GetBlocksDirPath(), additional_bytes_needed)) {
2011 |              InitWarning(strprintf(_(
2012 |                      "Disk space for %s may not accommodate the block files. " \
2013 | -                    "Approximately %u GB of data will be stored in this directory."
2014 | +                    "Approximately %u GiB of data will be stored in this directory."
2015 |                  ),
2016 |                  fs::quoted(fs::PathToString(args.GetBlocksDirPath())),
2017 | -                chainparams.AssumedBlockchainSize()
2018 | +                CeilDiv(additional_bytes_needed, 1_GiB)

hebasto commented at 1:46 PM on September 14, 2026:

The -prune option has MiB granularity. It seems weird to specify -prune=550 and then see a message saying, "Approximately 1 GiB of data will be stored in this directory."

l0rinc commented at 11:01 PM on September 23, 2026:

It seems to me the oddity is the -prune=550 target itself: during IBD, a target that small means repeatedly adding and pruning block files, and as #30037 notes, they may occupy almost 1 GiB near the tip anyway. The warning previously showed the full-chain estimate in GB. This patch shows the pruned estimate in GiB. I’m not sure a separate MiB warning is warranted, but I can adjust it if reviewers prefer.

Perhaps the GUI part can be fixed in a follow-up

https://github.com/bitcoin/bitcoin/blob/a49fa1f6e698430f9d8619cf769a514ae71fca5a/src/qt/intro.cpp#L300 is very similar and uses GB, but in #35948 (comment) @achow101 specifically said: I strongly prefer to use GiB rather than GB so the other updates should probably be done in follow-ups. Here I'm trying to focus on the free space estimates. Let me know if you have a better idea.

hebasto commented at 1:46 PM on September 14, 2026: member

The assumed blockchain size is maintained in GiB, but the first-run disk-space warning labels it as GB.

This change resolves the unit mismatch.

From #29678 (comment):

The GUI now uses "GB" (SI prefix) as a unit, based on the mindset of non-technical/non-CS users.

GB is standard for general audiences, and GiB for technical, scientific, or engineering contexts. I'd recommend keeping GB in the GUI.

In most scenarios, GUI users deal with the intro dialog to set their datadir and prune options for the first time. I think it's acceptable to keep "GiB" in the AppInitMain warning.

However, I've noticed that the Intro constructor in src/qt/intro.cpp actually accepts values in GiB while treating them as if they are measured in GB:https://github.com/bitcoin/bitcoin/blob/a49fa1f6e698430f9d8619cf769a514ae71fca5a/src/qt/intro.cpp#L151

Perhaps the GUI part can be fixed in a follow-up.