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2014/05/19 Btrfs-diff Between Snapshots
π 2014-05-19 01:01 in Btrfs, Linux

Differences between two btrfs snapshots

When you have historical snapshots, it may be useful to know what changed between 2 snapshots.

The best way to do this long term is to modify "btrfs send" to compute changes between the snapshots and just output the filelist instead of a stream with data.

However, until then, there is a hack that shows you files that got added and removed between two snapshots. It's not bulletproof like btrfs send, but it can give you a quick mostly working diff between two snapshots (*it will not show renames or deletes*). See more caveats on this original serverfault post.

legolas:/mnt/btrfs_pool1# btrfs-diff usr_ro.20140513_05:00:01/ usr_ro.20140514_06:00:02/ share/doc/linux-image-3.15.0-rc5-amd64-i915-preempt-20140216s1/buildinfo.gz share/doc/linux-image-3.15.0-rc5-amd64-i915-preempt-20140216s1/Buildinfo.gz share/doc/linux-image-3.15.0-rc5-amd64-i915-preempt-20140216s1/changelog.Debian.gz share/doc/linux-image-3.15.0-rc5-amd64-i915-preempt-20140216s1/Changes.gz (...)

You can download my latest snapshot of btrfs-diff. Note that I am not the author, it was copied from this serverfault post.

#!/bin/bash

# Author: http://serverfault.com/users/96883/artfulrobot # License: Unknown # # This script will show most files that got modified or added. # Renames and deletions will not be shown. # Read limitations on: # http://serverfault.com/questions/399894/does-btrfs-have-an-efficient-way-to-compare-snapshots # # btrfs send is the best way to do this long term, but as of kernel # 3.14, btrfs send cannot just send a list of changed files without # scanning and sending all the changed data blocks along.

usage() { echo $@ >&2; echo "Usage: $0 <older-snapshot> <newer-snapshot>" >&2; exit 1; }

[ $# -eq 2 ] || usage "Incorrect invocation"; SNAPSHOT_OLD=$1; SNAPSHOT_NEW=$2;

[ -d $SNAPSHOT_OLD ] || usage "$SNAPSHOT_OLD does not exist"; [ -d $SNAPSHOT_NEW ] || usage "$SNAPSHOT_NEW does not exist";

OLD_TRANSID=`btrfs subvolume find-new "$SNAPSHOT_OLD" 9999999` OLD_TRANSID=${OLD_TRANSID#transid marker was } [ -n "$OLD_TRANSID" -a "$OLD_TRANSID" -gt 0 ] || usage "Failed to find generation for $SNAPSHOT_NEW"

btrfs subvolume find-new "$SNAPSHOT_NEW" $OLD_TRANSID | sed '$d' | cut -f17- -d' ' | sort | uniq


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