See also GitHub issue #172.
QDirStat can break down the age of files (based on their modification time) in a subtree by year and, for the current year and the year before, by months. This is strictly for files; directories, symlinks etc. are disregarded.
This is a new view opened from the menu with View -> Show File Age
Statistics or with the F4 key. If a directory is selected, it starts with
that directory, otherwise with the complete subtree.
For each year, it shows:
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The number of files that were last modified in that year
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The percentage of those files relative to the selected subtree, both as a percent bar and as a number
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The total size of files that were last modified in that year
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The percentage of those files relative to the selected subtree, both as a percent bar and as a number.
For the current year and the year before, you can expand the months (click on the little arrows on the left).
The list always starts with the current year, even if there was no activity in the subtree in that year (i.e. no file was modified in that year). All inactive years up to the last year with any activity are displayed.
This helps to quickly see at a glance that there was a while with no activity, even without reading the year numbers.
Simply leave the File Age Statistics window open and click on another directory in the main window's tree view, and the File Age Statistics window is automatically updated with the data for that directory.
You can also switch that behaviour off when you uncheck the Sync with Main
Window check box at that bottom of the File Age Statistics window. In that
case, you can always simply hit the F4 key again to update the window.
If there are no more than 1000 files in the selected year or month, you can use the Locate button to open another pop-up window that lists those files. Click on one of them to select it in the main window; the main window scrolls to that branch, selects the file and updates the Details panel with it.
This is limited to 1000 files because it becomes very unwieldy at some point, and performance suffers heavily. If you find yourself wanting to see more than 1000 files in a subtree, break it down to deeper subdirectories (see above).
This view was inspired by the discussion in GitHub issue #165 where an admin requested this for his users that had accumulated large amounts of data and lost their overview.
It had become necessary to move some of those data to archive media, but the users had lost the overview what was current and what was not, i.e. which parts were good candidates to be moved to archive media.
Imagine a large machine with a large storage array used by a great number of scientists collecting research data over many years. Researchers come and go; new ones take over their projects and their data for their research. Others leave when they are finished with their degree. Even with a best effort of documentation (which is wishful thinking to begin with), after some time it becomes murky what set of research data is what, and which of them are in active use. Somebody new will not dare to get rid of anything; even if that only means moving it to archive media where it's less easily accessible.
While this File Age Statistics is by no means a general solution, it can contribute to regain some kind of overview: If a directory branch has been completely unmodified for many years, this is an indication that it may not be in active use.
Of course, this is not guaranteed: It is very well possible that they are actively using the data sets from 1995, 2000, this year and the year before, and the old data sets are a reference that does not change. Only the users can really tell. But the file age may give them additional hints.
It depends on the use case which columns in the File Age Statistics are more important: The number of files in that year (or month) or their total size. That's why both of them are displayed.
When it comes to the relevance of data in a subdirectory, the sheer number of
files may be important: Even a lot of small files that accumulated may distract
and get in the way, especially when scripting (find commands come to mind)
over large directory trees.
When that is not an issue, but disk space is running out, of course the total size of those files may be more important.
One use case is showcased in GitHub issue #172:
A photo collection that grew over the years. In that case, the number of files is much more important than their total size: During those years, camera technology rapidly advanced, moving from 3 Megapixels up to 10, then 12, then 24. That means that photos taken in earlier years with considerably less Megapixels are of course much smaller, so for photo activity during those years the size is not a good measure; but the number of photos per year is.
Start at the top of the subtree. Arrange the windows so you can see both the important part of the main window and the File Age Statistics window.
If the File Age Statistics for the toplevel don't give a good overview (which is likely), click on its first subdirectory in the main window's tree view. Watch the File Age Statistics window.
Then use the Cursor Down key in the main window to go to the next subdirectory. Watch the File Age Statistics window; but it's enough to give it just a glance: Watch how the inactive years (the greyed-out entries) change. Move to the next subdirectory etc.; you will now have a first impression on the age distribution among that first subdirectory level.
If that also doesn't shed much light, go to the next deeper subdirectory level in the main window. Since the main window's tree view orders the directories by size by default, starting from the top is most promising.
If repeating that over several subdirectory levels still doesn't give you an overview, this may not be the right tool for the job; it's not a catch-all solution for every situation.
Don't forget that there are also actions in the Discover menu to immediately find the oldest and the newest files in a directory tree. This is meant for individual (or at least small numbers) of very old or very new files.
In the main window, the Last Modified tree column shows the latest modification time in that subtree, but in including directories and symlinks. That may or may not be what you need; it depends on the task.
Notice that a directory's modification time is updated whenever a file is created or deleted there, or whenever a file is moved to or out of that directory.
This may be little known since it is not enabled by default, but there is a similar column Oldest File in the main window's tree view that shows the modification time of the oldest file (not directory, not symlink) in that subtree. This may be useful to drill down the tree view for very old files.
To activate that column, switch to an appropriate main window layout (preferable L2 or L3), right-click on the headers of the tree view to open the context menu, then select Hidden Colunns -> Show Column "Oldest File".
This functionality may be superseded by the relatively new Show Oldest Files action in the Discover menu.