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CognitionAI
blockdiff
Rust2025–2025
CognitionAI / blockdiff

blockdiff

Fast block-level file diffs (e.g. for VM disk images) using CoW filesystem metadata

Systems & InfrastructureCreative & Media
Explore on GitHubRead Hacker News discussions
2Distinct people
2Mentions
0Explicit recommenders
263GitHub stars
REPOSITORY AT A GLANCE

What to know before exploring

What it is

Fast block-level file diffs (e.g. for VM disk images) using CoW filesystem metadata

GitHub

Where it is used

No documented product use has been verified yet.

What people are saying

No recommendation phrase was found in the indexed comments.

No classified warning is attached to this page. Read the discussions before treating silence as approval.

Also in these discussions

No other repository is repeatedly linked in the same discussions.

This week on Hacker News

Nov 7–Nov 14 UTC · Direct repository links and separately labeled related project stories. Indexed through 11/14/2026, 1:49:46 PM UTC.

No direct repository links were found in the indexed HN discussions over the past seven days. Older discussions are available below.

Mentions over time

HN mentions by week2 dated mentions

Observed mentions: 2025-06-23 18:44:53 UTC to 2025-10-01 10:23:19 UTC. Weeks start Monday, UTC.

012025-06-23 00:00:00 UTC to 2025-06-30 00:00:00 UTC (exclusive): 1 mentions; 1 submissions, 0 commentsJun 232025-06-30 00:00:00 UTC to 2025-07-07 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-07-07 00:00:00 UTC to 2025-07-14 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-07-14 00:00:00 UTC to 2025-07-21 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-07-21 00:00:00 UTC to 2025-07-28 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-07-28 00:00:00 UTC to 2025-08-04 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-08-04 00:00:00 UTC to 2025-08-11 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-08-11 00:00:00 UTC to 2025-08-18 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 commentsAug 112025-08-18 00:00:00 UTC to 2025-08-25 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-08-25 00:00:00 UTC to 2025-09-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-09-01 00:00:00 UTC to 2025-09-08 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-09-08 00:00:00 UTC to 2025-09-15 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-09-15 00:00:00 UTC to 2025-09-22 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-09-22 00:00:00 UTC to 2025-09-29 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-09-29 00:00:00 UTC to 2025-10-06 00:00:00 UTC (exclusive): 1 mentions; 0 submissions, 1 commentsSep 29

Counts come from the repository’s dated source evidence. Index cutoff: 2026-11-02 08:16:59 UTC.

View mention counts and date ranges
UTC ranges include their start and exclude their end. Select a period to filter the source evidence.
PeriodStart (UTC)End (exclusive, UTC)MentionsSubmissionsComments
Jun 232025-06-23 00:00:00 UTC2025-06-30 00:00:00 UTC110
Jun 302025-06-30 00:00:00 UTC2025-07-07 00:00:00 UTC000
Jul 72025-07-07 00:00:00 UTC2025-07-14 00:00:00 UTC000
Jul 142025-07-14 00:00:00 UTC2025-07-21 00:00:00 UTC000
Jul 212025-07-21 00:00:00 UTC2025-07-28 00:00:00 UTC000
Jul 282025-07-28 00:00:00 UTC2025-08-04 00:00:00 UTC000
Aug 42025-08-04 00:00:00 UTC2025-08-11 00:00:00 UTC000
Aug 112025-08-11 00:00:00 UTC2025-08-18 00:00:00 UTC000
Aug 182025-08-18 00:00:00 UTC2025-08-25 00:00:00 UTC000
Aug 252025-08-25 00:00:00 UTC2025-09-01 00:00:00 UTC000
Sep 12025-09-01 00:00:00 UTC2025-09-08 00:00:00 UTC000
Sep 82025-09-08 00:00:00 UTC2025-09-15 00:00:00 UTC000
Sep 152025-09-15 00:00:00 UTC2025-09-22 00:00:00 UTC000
Sep 222025-09-22 00:00:00 UTC2025-09-29 00:00:00 UTC000
Sep 292025-09-29 00:00:00 UTC2025-10-06 00:00:00 UTC101

What Hacker News says

2 sources
silasalberti·Jun 23, 2025Submission

Show HN: Blockdiff – How we built our own file format for VM disk snapshots

Usually, I’m a researcher working on areas like RL for coding agents – but one day I became annoyed by our slow VM startup times. So I took the plunge into systems engineering and built the first version of our VM hypervisor called otterlink. It now powers both our research & all of Devin production workloads. Compared to EC2, otterlink was able to bring down VM startup times by about 10x. The real pain point, however, were EC2’s long snapshot times. We want a lot of flexibility (e.g. forking, rollback and suspending VMs) that all require taking disk snapshots. On EC2 taking disk snapshots usually took a whopping 30+ minutes, which would be a terrible experience for our users. With otterlink we were able to bring this down to just a couple of seconds – a 200x speed-up. To achieve this, we built our own file format blockdiff for instant bl
Read the rest
ock-level diffs of VM disks. Creating block-level diffs of two files is a much broader problem that goes beyond VM disks. We assumed there must be an existing open-source solution. To our surprise we couldn’t find such a tool, so we’re open-sourcing our implementation today: https://github.com/CognitionAI/blockdiff
11 points · Open discussion

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