borgbackup/borg

restore big files/block devices with considering already present data

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#5638 opened on Jan 20, 2021

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 (5 comments) (0 reactions) (1 assignee)Python (10,086 stars) (732 forks)batch import
cmd: extractenhancementfilesystemhelp wanted

Description

I use borg to make backups of my LVM volumes. It works fine at backup creation time but not as good when I do 'borg extract'. It pulls many gigabytes of data from remote borg repo server although I still have an almost unchanged device in place.

It would be nice to have an option to not just extract data from a borg repo but to also check against an existing file/block device, if it already has the required data and only retrieve changed data from the remote repo.

Contributor guide

Tech stack
python
Domain
backenddata
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
understanding of borg's extraction mechanismPythonblock device handling
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
Investigate the borg extraction code in borg/archive.py and borg/extract.py. Understand how current extraction works and how to add an option to compare existing data before fetching chunks from remote. Review the issue comments for any prior discussion about implementation details. The feature requires modifying the extraction pipeline to check local data and only fetch missing or changed chunks.