I'm using Ubuntu 25 with the BTRFS file system and recently cleared out a ton of space by deleting large `~/.cache` folders (around 20GB each for two users). After doing this and restarting my system, I expected to see the available space increase, but it actually decreased from about 45GB to 33GB. I've checked that the Trash is empty and there's only about 100MB in `/tmp`. When I used `Filelight`, it accurately showed much less data in my home folders now, but when I ran `btrfs filesystem df /`, the output still indicates that most of my space is used up. So I'm curious, where did my free space go?
4 Answers
I’ve seen similar issues before. It could be that the snapshots you've mentioned are still tied to the data you deleted. Even if they’re old, the data might still count against your used space.
Have you checked if there are any BTRFS snapshots still holding onto the space you thought you freed? Sometimes old snapshots can retain deleted files, affecting the available space you've freed up.
For BTRFS, skip the usual `df` and `du` commands; try using `btrfs filesystem usage /` or `btrfs filesystem df /` instead. They provide more accurate info on what’s actually happening with your disk space.
I checked `btrfs filesystem df /`, and it still doesn't show additional space. Shouldn't all these features be seamless for the user? I removed some old snaps too, but no changes are showing.
Exactly, those features should ideally be invisible, just like on other platforms. It's frustrating when you’re not seeing the expected free space.
When you're using BTRFS, it employs a copy-on-write (CoW) feature that can cause a delay in updating the free space displayed. Even after you've deleted files, the disk space reports might not reflect this change right away because of how the file system operates. It’s worth waiting a bit and checking back later.
Would running the `sync` command help clear up the space? I’m unsure, but maybe that would trigger the update.
I thought CoW and snapshots were supposed to be transparent for users. Why isn't the deleted space being reported like it would be on other systems?
You're right, the age of snapshots doesn't matter. What counts is whether they still contain data that should have been cleared.