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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)
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Gnome Disk Usage Analyzer is a GUI program with similar purpose as du and ncdu.

I haven't used it in a long time, but I believe caches scan results. Subsequent scans should become faster, barring unexpected cache invalidation (which, granted, is "hard CS problem").

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Only a partial solution (3 comments)
Only a partial solution
Karl Knechtel‭ wrote 4 months ago

As it happens, I have this program (Baobab) included with my system. It only gets me a small part of the way there. It "caches", but only within a given run of the program - it doesn't persist that data. (Of course, storing the cache could itself invalidate a small part of that data; but I'm pretty sure I can see an algorithm that would localize the effect.) Also, it only ever scans an entire drive; I can't start by asking it only about a specific folder.

matthewsnyder‭ wrote 4 months ago

I would assume that when it's busting the cache for / for example, it would only re-scan the parts that changed. It would be very silly if it scanned the whole drive because just one file changed.

I guess baobab doesn't solve your problem then, sorry. Hopefully someone else will find a solution. I'll leave this answer here, since it might at least be helpful to another reader.

Karl Knechtel‭ wrote 4 months ago

What I mean is that if I quit and restart the program, it will re-scan everything. Nothing is, as far as I can tell, persisted between separate runs of the program.