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Comments on Efficiently determining disk usage of a folder (without starting from scratch every time)

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Efficiently determining disk usage of a folder (without starting from scratch every time)

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When I use my computer, one question I commonly want to answer for myself is "how much space is being used by the contents of this folder?". Typical file/window managers, IMX, answer this question the same way that Windows does: by recursing over directory contents and summing their logical sizes. This doesn't suit my needs, for three reasons:

  • While the logical size of an individual file is interesting to me, a sum of logical sizes is not; I want a sum of physical sizes, because the question is about disk usage.

  • It does the calculation (and directory traversal) on the fly, and doesn't show a progress bar or even a clear indication that it's done. Sometimes the file count and size sum will pause for seconds at a time and then start increasing again.

  • It's very slow.

I know that I can use du at the command line to get physical sizes, and it's clear when du is finished because it outputs to the terminal and eventually returns to a terminal prompt. However, it doesn't solve the performance issue.

Is there a filesystem that natively caches this information about directories, or well-known software that maintains such a cache - so that if I e.g. check the size of /home/user, the size of /home/user/Desktop is already known and can be returned instantaneously (as long as the subfolder hasn't been modified in the mean time)? Similarly, caching the result for /home/user/Desktop should speed up a later check for /home/user, since it wouldn't have to consider the Desktop contents. It would also be nice to have a GUI for such a program.

I thought about making such a program, but I don't want to reinvent the wheel. I'd also be interested if there's any way to make ext4 filesystems cache this information automatically, even though they don't appear to by default.

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3 comment threads

File system dependent (2 comments)
What do you consider slow? (5 comments)
Links (hard and symbolic) (3 comments)
Links (hard and symbolic)
Karl Knechtel‭ wrote 5 months ago

I understand that files could be hard-linked in multiple places within the file system, which raises questions about how to account for them (i.e., which folder counts as "responsible for" the disk usage for that file, or if that usage should even be considered shared between multiple containing folders). But I think that's out of scope for this question - for now let's suppose that I don't care about how this is accounted for. I have a separate question in mind specifically about hard links.

Symbolic links are trivial here IMO: just count the file itself, without following the link.

matthewsnyder‭ wrote 5 months ago

du which you have mentioned has switches like --no-dereference, --count-links and --one-file-system for dealing with links as well as mounts. Are these enough for you, or do you want something more sophisticated?

Karl Knechtel‭ wrote 5 months ago

Those help with accounting for hard links specifically, but not with the overall question here. Although I'd like to be able to get at the actual system call for the link count in order to do more sophisticated things; but that's a separate question.