When Arq Backup’s hourly backup runs every two hours

This post will talk about two more design decisions in Arq Backup 5 that I disagree with. One annoying, the other serious. They’re both in Arq’s scheduler.

Let’s start with the annoying one.


In the screen capture above you can see Arq’s minimalist options. You can select to back up every n hours and any minute past the hour, daily at any hour on the hour, or manually.

If you have multiple backups and want to spread the load, depending on the duration of the average incremental backup, perhaps you’ll choose :00, :15, :30, :45, or something similar. But Arq has what I consider to be an error in the calculation to schedule the next backup. I discussed this with support and they informed me it was design intent, so you’ll have to decide for yourself which way you think it should work.

Without presenting the debug logs that helped me figure this out, suffice it to say that the later in the hour you choose to run the hourly backup, the more likely it is to run at n+1 hours. If you’ve chosen to run every hour at :59 past the hour, and you have more than one minute’s worth of files to back up, then I guarantee you that your backup will run every two hours. If Arq finishes an hourly backup in the next hour, it’s considered to have already run that hour and won’t run again. This is a design decision to prevent a backup from running continuously if it finishes in the hour, let’s say at :16 past, but was scheduled to run at :15, it would run immediately. By not allowing more than one run per hour, Arq prevents this tragedy.

But it’s not a tragedy at all, is it? It’s my responsibility to set the backup frequencies and ensure they don’t run continuously. I don’t want the program making that decision for me because in the case of choosing to run near the end of the hour, Arq is saying, “You’re not going to run hourly, and you can’t make me.”

Nothing in Arq’s documentation will warn you of this design choice. You have to discover this for yourself when you realize that your important data isn’t being backed up every hour like Arq said it was going to do in the preferences panel.

My workaround? Run all backups early in the hour. Yup, that’s all I can do until Arq decides to trust the users that we really know what’s best for us.

But worse…

The second design defect related to scheduling backups is that “Pause backup between” option. Since it appears for every destination, one would logically conclude that it applies to the individual backup set. But you would be wrong.

The option allows you to pause backups on the hour between a start and end hour. I think it’s an unnecessary restriction to be only on the hour, but I could live with it. If it worked as expected.

I don’t know if this is a bug or another strange design decision, but in my experience, if I want to pause a backup between 02:00 and 07:00 what actually happens is that the backup for which that option is set still starts to run (you can see it in the backup logs), and then it pauses. But Tom, you say, that’s what it’s supposed to do. Well no, it shouldn’t even start to run. You see, because Arq Backup doesn’t run backups concurrently, once any backup has started, no other backup will run until the currently running backup completes, no matter how long it takes. It can run for weeks and halt all other backups.

So when the backup starts running at 02:00 and immediately pauses until 07:00, no other backups will run. All the other hourly or daily backups set to run past 02:00 won’t run until after 07:00. This is effectively a global pause even though it’s set on an individual backup set. I didn’t even try to see what would happen if I had more than one set configured to pause. I shudder to think.

Live with it

None of the behaviour of what I’ve described above could I find in the manual. Arq’s manual is not geared towards professionals who want and need to understand exactly how their backup software works and don’t want to use trial and error to discover behaviour that should be in the manual. It’s targeted at users who just want to set up one or two simple backups and forget about it. That’s fine, that’s probably the market they’re targeting. Just manage your expectations.

I’m living with Arq’s design decisions, but I don’t like them. I hope this post helps you understand if you can live with those decisions too.

Author: Tom

Destroyer of software. If I haven't tested it, it hasn't been tested.

4 thoughts on “When Arq Backup’s hourly backup runs every two hours”

    1. I don’t recommend any backup software. Every person’s needs are different and may be served better by the different apps out there. They vary quite a bit in capabilities.

      The best I can say is that, in spite of some pretty serious scalability issues and annoying design decisions, I’m living with Arq because it suits my needs the best of all the options out there. I wish there was something better and I hope Arq 6 fixes the issues I’ve reported on this site, but I’m sticking with it for now.

  1. I just encountered the “pause everything” issue today (2017-12-01).

    I have an outgoing sftp backup that runs to a remote location in addition to local attached storage backups and a remote backup to Wasabi. I thought that limiting the traffic to our remote location during working hours would be a good idea, but today while looking through our logs I see that the local backups and the Wasabi backups are also paused due to this setting.

    This seems like a poor implementation of scheduling logic.

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