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Incremental Backup with Rsync

Notes on using rsync to implement incremental backups, using hardlinks to save space.

From: http://www.mikerubel.org/computers/rsync_snapshots/

TODAY=$(date -I)
FIRST_BACKUP="2017-12-18"

cd /mnt/archive/backup
rsync -a --modify-window=1 --link-dest=$FIRST_BACKUP /mnt/Antonio/data $TODAY --log-file=$TODAY.log

Option --modify-window

The --modify-window option solves problems of timestamps inaccuracy on windows resulting in deleted or re-backuped files.

Files checksums

Files are considered existing in the backup (and thus hard-linked instead of copied) if name and timestamp are equal, no checksum is computed by default. To enable checksum use -c.

Why --delete is not needed?

From: http://dev-notes.eu/2015/06/incremental-backup-on-server/

I originally used the --delete flag on this script - thinking that it would be necessary to keep the latest incremental backup synchronised with the current source filesystem.

However, --delete has no effect when syncing into an empty directory, which is basically what happens when using the --link-dest method of rsync. The directory specified by --link-dest is used as a reference point, and any files in source that are unchanged relative to this reference point are hardlinked to their exisiting inode in the reference directory.

Other references

https://github.com/xolox/python-rsync-system-backup https://github.com/Nextpertise/autorsyncbackup https://github.com/seanh/snapshotter