Reliability of Duplicati 2.0

I know this is going to sound a bit harsh… But it’s nevertheless question no. 1 when talking about backup software: How reliable is Duplicati 2.0?

We’re currently in the decision process about what backup software to use on our Windows machines in the future and found, that some of our users were using Duplicati 1.3.4 before - so it seems natural to check Duplicati 2.0. We’re talking about Windows machines only, on Linux machines we rely on Borg and are very happy with it. However, Borg isn’t available for Windows (resp. requires “hacks” like WSL), so it isn’t on the table. Duplicati 2.0 sounds very, very promising!

However, since Duplicati 2.0 isn’t compatible with Duplicati 1.3.4 we had to move all old Duplicati 1.3.4 backups to a new platform, requiring us to restore all old backups and creating new ones in the process. It was a disaster. I’m not going to mince matters here, so please excuse the harsh words, but Duplicati 1.3.4 is the worst backup software I’ve ever seen. Thus I’m pretty skeptical towards Duplicati 2.0 whether it meets its promises - Duplicati 1.3.4 made a lot promises, too, but didn’t deliver. But I’m still very open to Duplicati 2.0 - Duplicati 1.3.4 is old and I don’t want to generalize my experiences. However, due to my experiences I have very specific questions:

First of all it was close to impossible to get Duplicati 1.3.4 running. I know, you guys no longer support Duplicati 1.3.4 and this is totally fine, but since you decided not to maintain BC, I must be able to run it somewhere at least. Backup software is long-term software, restoring a 10 years old backup must not be a problem. Since I couldn’t run Duplicati 1.3.4 on newer machines I tried virtual machines. A VM with Windows XP or Windows 7? No chance, Duplicati can’t restore from network drives and copying 720 GB compressed backups to a VHD is no option. So I tried Ubuntu 14.04. Duplicati’s CLI is rather… unorthodox to use. But after a lot of pain I got it working.

Out of 73 backups of a single machine (16 full backups, 57 incremental backups) there are just 3 backups (sic!) that had no errors. When ignoring errors which were caused by Duplicati not being able to restore symlinks, there are 20 close-to-fully-restored backups (10 full backups, 10 incremental backups). Most errors were caused by corrupt volume files, not just yielding all following incremental backups useless, even yielding all following data in the same backup useless (for example, the first volume of a 22.64 GB full backup was corrupt, yielding the whole (!) full backup as well as the following 4 incremental backups useless). Another very common error was Duplicati failing to restore a diff or snapshot file. Restoring 720 GB of compressed data took about 7 days, running 24/7, even though 35 backups failed somewhere in the process due to corrupted volumes. I mean… Wow… A 27% success rate in >160 hours.

To be fair, we’re talking about Duplicati 1.3.4. It’s a kinda old software and the stuff I read about Duplicati 2.0 looks promising. However, the fact that you guys still don’t consider Duplicati 2.0 stable (according to Wikipedia you focus on Duplicati 2.0 since 2013?) and Duplicati 1.3.4 was a total nightmare, I’m not so sure about whether I can really trust the promises made on the website. Thus I want to ask for honest feedback, whether the issues of Duplicati 1.3.4 have been fixed in Duplicati 2.0.

  • Is Duplicati 2.0 stable? You guys promote it as the only supported, yet not stable (beta) version of Duplicati. According to Wikipedia you focus on Duplicati 2.0 since 2013, so it’s 7 years in which Duplicati 2.0 still didn’t reach a stable version. What’s the reason for this?

  • How much of Duplicati 1.3.4’s code base is still present in Duplicati 2.0?

  • What about long-term support? I must trust Duplicati to be able to restore my backups in 10+ years - either by still supporting old backup formats or by providing a platform that can be used to restore my backups using a old version of Duplicati 2.0. Duplicati 1.3.4 didn’t run well in virtual machines since it couldn’t use network shares to access files. What about Duplicati 2.0, can I run it on a virtual machine with Windows 10, even though it’s 2030? What are the long-term support plans?

  • What does Duplicati 2.0 do to recover corrupted backups? We’re talking about long-term backups, it’s kinda common that one or the another bit flips in 10 years. Is Duplicati 2.0 able to recover from these situations? Or is the data thrown away? If it is thrown away, how much data is thrown away (the whole corrupted backup plus n following backups? “just” the backup? a multiple hundred MBs large volume? or just a small chunk of a few KB?)?

  • How fast is Duplicati 2.0? Recovering 73 backups with a total compressed size of 720 GB within >160 hours is unacceptable. How much time does Duplicati 2.0 take for this - assuming everything is stored on a common HDD?

  • What issues did you guys experience in production in the past? This includes both already fixed and still unfixed issues. Did you guys loose backups in the past due to bugs? How hard was it to recover corrupted backups? No software is perfect, I rather want to know how common issues are and how easy they could be solved.

  • What do you guys do when someone (like myself) asks you for help about a 10 years old backups? Tell me it was made with a now unsupported version? Or try to help me with disaster recovery, even though you naturally won’t release a fixed version of such a old milestone?

Thank you for your time and feedback! :heart:

1 Like

Nobody? I guess no answer is also an answer :unamused:

Hi @PhrozenByte

I’m not into development but found this post helpful:
Is Duplicati 2 ready for production?

Maybe you should keep in mind that Duplicati is developed and maintained from professionals in their sparetime. For a business usecase like yours I personally would flock to some of the payed enterprise solutions including insurance on data loss and big support teams.

That said you may find some posts in the forum with similar scenarios who’s authors are able to share their experiences with Duplicati 2

1 Like

To add to that, the main author of all Duplicati versions has very little time lately, thus is unlikely to jump in. There was more activity earlier. GitHub Contributors history shows that very few go back to the beginning.

Speaking for myself, 1.3.4 is too old, 2.0 stability is too subjective, and questioning honesty put me off…
My usual answer to why progress is not fast (at least for features) is that there are few people available.

As you might know, getting obscure hard-to-reproduce bugs out of complicated software is very difficult.
At some point you call it stable but it’s still not perfect. No software is. Best practice is multiple methods.

1.3.4 is ancient history to most people here. Old news articles talk about some of the changes from 1.3.4.
Block-based storage engine is on current web site, and it links to a whitepaper describing the new design. is 1.3.4. If you want code comparison, have at it…
There’s probably a huge amount of code moving (if not total rewriting) due to the new core design for 2.0.

I kind of like the suggestion by @Ralf that a paid solution “might” do better for you, however even very big companies do eventually end support. I don’t know whether any have specialized tools, e.g. just to restore.
Independent restore program is Duplicati’s offering, which is still subject to Python and dependencies drift.
How the backup process works and How the restore process works (and lower-level docs) cover designs.

You can certainly put your specific configurations on a virtual machine, test it works now, then document it. Duplicati 2.0 backups are completely portable between different destination storage, and that will also help.

Duplicati maintains records of all backup destination file hashes, and has a variety of ways to test some or verify all files (DuplicatiVerify.* scripts do need local access). So there’s some ability to detect file damage.

Disaster Recovery is a lab demo of intentionally corrupting backup files then using Duplicati recovery tools. You can see the progression. Sometimes you just purge some files. If things go way off, there’s a tool that forgives more types of damage, but Duplicati.CommandLine.RecoveryTool.exe is for emergency restores.

You can search the forum for when it was last pulled out, but IIRC it was around the start of 2020, and the Usage statistics for Duplicati show about 3 million backups per month. Not ALL complain to the forum. :wink:

Support forums and issue trackers tend to gather issues, although big issues will make people just leave.

Big Comparison - Borg vs Restic vs Arq 5 vs Duplicacy vs Duplicati gives some insights. Try it yourself…

The little known (and it may stay that way) Duplicati FAQ has a 2014 entry by lead author which explained:

Q : Is 1.3.x dead?

A : Yes. We do not have the man-power to maintain 1.3.x and develop 2.0. You can continue to use it, but we do not develop on it ourselves, as we have chosen to focus on 2.0. Feel free to checkout the 1.3.x branch if you want to continue the development of that version.

So that’s the history, and future is unknown. Perhaps some large vendor can give you a credible answer?

This was a big concern for me when I was looking around for CrashPlan alternatives. I did not like that CrashPlan could decide on a whim to end the product and it would no longer function. I decided I needed something more under my control. Duplicati fit this bill - it is open source, there is no server side component out of my control, and the storage can be anything I wish.

Development is ongoing but admittedly slower than many of us would like. As others have pointed out, it is largely a volunteer effort. But worst case - if all development were to cease - Duplicati would still work. If development was never resumed, I’d probably be forced to migrate to another platform at some point. But the existing version could still be used to access the older backups, as needed.

1 Like

Hopefully this wouldn’t happen with cloud storage with its extremely high durability rating. You can even protect against “bitrot” yourself with higher end filesystems (ZFS or Btrfs) that do data checksumming and auto healing. Otherwise basic RAID may even help protect against it, although there is some question if the RAID subsystem would detect a random bit flip if not accompanied by a read failure by the hard disk. These reasons are why I’m a big fan of ZFS or Btrfs or cloud storage.

At one point there was some discussion about adding native Parity to Duplicati back end data. See PR #3879, but it has since been closed due to lack of activity.

But if corruption does occur, Duplicati has methods to detect this and recover from it. You may lose the ability to recover some data though. If a dblock becomes unrecoverable then all backup data referencing that block will be affected.