Monday, May 4, 2020

Arq and Time Machine Exclusions

Manuel Grabowski:

I figured there must be some way to find out what data exactly changed inbetween two TM snapshots. There is. I let that script run (for almost an entire day) and in the resulting output I was quickly able to find the directory that was responsible for almost the entire size of the changes: ~/Library/Arq/.


So for months, my two primary backup strategies have negatively affected each other by slowing down to a grinding halt and consuming ungodly amounts of CPU power and fan spinnage.

The corresponding folder in Arq 6 is /Library/Application Support/ArqAgent. Even though I recently started new Arq backups, and they contain only a small fraction of my files, that folder already contains a cache.noindex folder that’s 11 GB. (Due to its file permissions, that folder is no longer accessible in Finder, so I had to inspect it via Terminal and sudo.)

Because .noindex only applies to Spotlight, Time Machine is wasting time, energy, and space backing up these files. To exclude them from Time Machine, they’d have to be in a .nobackup folder or otherwise marked.

I suppose there’s a reason that some people might want to back up the Arq cache. It could be slow or expensive to redownload the cached data if you do need to restore from a backup. But I decided to add a manual exclusion in the Time Machine preferences.

Sidenote: I’m now using Arq 6.2.11, which seems to work well except that unmounting an unrelated drive still causes other in-progress backups to abort.


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Because the Arq 6 cache folder was not visible in the Finder, I wasn’t able to exclude it from Time Machine in the usual way. Here is what I did:

1. Grant Full Disk Access to Terminal (you can remove this when you are done). Do this in System Preferences → Security & Privacy → Privacy tab → Full Disk Access.

2. From a Terminal prompt:

sudo tmutil addexclusion -p "/Library/Application Support/ArqAgent/cache.noindex"

3. To verify that it worked:

sudo tmutil isexcluded "/Library/Application Support/ArqAgent/cache.noindex"

(you should also see it in the Time Machine Preferences pane where it shows all your excluded items)

Sören Nils Kuklau

I figured there must be some way to find out what data exactly changed inbetween two TM snapshots. There is.

Semi-OT: for those who prefer a GUI, I’ve been using BackupLoupe for this for many years. (My main goal seems similar: see if recent backups are particularly large, and if there’s no plausible reason such as a system update, dive into why that might be.)

It does have the same awkwardness with network volumes, though. I wish macOS handled those as transparently as Windows does.

@Nate Yeah, to be clear, I just excluded the whole ArqAgent folder using the GUI. Good tip!

Oh wow, my cache.noindex for Arq 6 is 37 GB!

…and it seems like 25 GB of those are the ArqAgent/cache.noindex/storageLocations/2/arq5/packsets, maybe a leftover from the not-so-great Arq 5->6 upgrade?

"Sidenote: I’m now using Arq 6.2.11, which seems to work well "

Do you think it successfully deduplicates between two or more different backup sets from one computer to one destination? I ask because each backup set has its own folder structure on the destination.

@gilby I don’t think so (and I don’t think I would want that).

Stefan Reitshamer

Arq 7 only aborts a backup plan when the drive being unmounted is involved in the plan. If it's backing up driveA and you unmount driveB, it won't abort.
Lots of other improvements too, including a native UI.
It's in pre-release now for macOS.

Ironic, I found this page because I saw that Arq itself is backing up this directory...

Continued from above...
To be more precise, not the directory you refer to but:


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