Dar used by John Goerzen

Who

John Goerzen is the maintainer at Debian of dar, libdar and libthreadar software.

He first explored a lot what was possible to do with and around dar and in particular he shared his finding on how to use dar as an asynchronous rsync

Context

I use dar to back up almost all of my non-zfs systems. This includes Raspberry Pis, laptops, other smaller systems, and VMs in the cloud.

Start date

for a long time

Backup/archive size

unknonwn

Media used

I use Dar in conjunction with NNCP to transmit the backups asynchronously to the backup system.
This allows daily backups to be captured even at moments when the system isn't connected to the Internet or has poor connectivity. Then the batches of dailies can be transmitted when connectivity is restored.
I also use Dar for archiving. I periodically burn BD-Rs with important records (tax records, etc) and use dar for that.

Why dar

On systems that run btrfs, I take a btrfs snapshot and back that up with dar. On the target, these are unpacked in order (using my filespooler program) and history is maintained using zfs snapshots on the backup system.

I have scripts that save off a catalog on the local machine being backed up, and then after that first full backup, always send incrementals.

For a long time, I combined this with mtree, which is a tool from the BSDs that will scan a directory tree and record metadata (size, mtime, etc). I would use this to periodically verify that the target matches the source, since the incremental chain was effectively hundreds or even thousands of backups long. More recently, I've realized I could just isolate the catalog from incoming archives and compare against that.

I also put Windows and Linux binaries on every disc to make recovery easier (Plus DarGUI for Windows).

I also have hard drives that I use for archiving, for things like family photos and such. I use dar to store a full backup and then incremental dar files as well, updating it about once a month. Every few years, I restart the chain from scratch.

As I have started to explore dar more, I have also learned it is a nice replacement for some other tools. For instance, btrfs doesn't have something like "zfs diff". But I can create a dar isolated catalog from one snapshot, and then compare the state of another. This replaces tools like mtree from BSD.

other remarks

I wrote a comparison of backup and archiving tools

Source

John Goerzen, in December 2025

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