How to reclaim disk space used by Docker volumes, but keep a few important on

It is a sparse file: copying it is very fast when it's empty. I don't know if the OS recognizes the space claims, but it would be logical if it did so.

I took a brief look at the issue and it's very strange. People reporting the issue and piling on clearly don't understand sparse files (which is fine in and of itself), and their claims that "the rest of the system treats the spare file as regular file" are just not very credible to me.

The thing is, if you want to look at the physical size of a file/directory, you don't use ls, you use du. Similarly, if you want to look at disk usage and free space on a volume, you use df, not summing up ls reported size of all files. Using df for free space is especially important on APFS since you have APFS volumes sharing the space in a container. And of course, du and df correctly report actual disk usage. If you check Docker.raw in Finder, it says something like "63,999,836,160 bytes (10.25 GB on disk)", too. Btw, even `ls -l` reports correct total disk usage:

  $ ls -lh ~/Library/Containers/com.docker.docker/Data/vms/0/data
  total 9.6G
  -rw-r--r-- 1 <omitted> staff 60G Jun 17 02:01 Docker.raw

There's just no way "the rest of the system treats the spare file as regular file". I suspect people actually have disk space tied up in APFS snapshots (Time Machine takes a lot of those and I have to clear them constantly with tmutil on machines with meager SSDs), but they're not aware of that, instead they ran some crappy script or something found online, located this "huge file", then just blamed it for the disk usage. Any proper tool, e.g. Disk Utility (builtin), DaisyDisk won't make this obvious mistake. I thought maybe people were using Finder search to find large files and that's the problem, but I just tried and Finder search also makes a distinction between logical size and physical size, so it's not even that.

Edit: In case it's not clear, sparse files don't "reserve" their space. Try this:

  for i in {000..999}; do dd if=/dev/zero of=/tmp/sparse-$i bs=1024 count=0 seek=104857600; done

You just created a thousand 100GiB files totaling zero bytes in disk usage (not counting metadata).

I’m not sure why you’re being downvoted but your comment doesn’t address the issue. Of course Docker will need some pre-allocated space but setting it so high as default seems excessive and ignores the real problems it’s causing to people in that issue thread.

docker-compose logs -f <service>

So you don't have to manually hunt down the container you want the logs for.

I guess - and I might be very wrong here - that the reason for client / server architecture was to be able to schedule docker containers on several hosts without the need to ssh into them. And I guess something like docker-in-docker or docker containers accessing the Unix socket would be more complicated.