Make grown extracted tar file small again

[this answer is assuming GNU tar and GNU cp]

There is absolutely no diff and the checksum is the exact same value. Yet, one file is as twice as big as the original one.

1.1M    /path/to/old/folder/subfolder/file.mcapm
2.4M    /path/to/extracted/folder/subfolder/file.mcapm

That .mcapm file is probably sparse. Use the -S (--sparse) tar option when creating the archive.

Example:

$ dd if=/dev/null seek=100 of=dummy
...
$ mkdir extracted

$ tar -zcf dummy.tgz dummy
$ tar -C extracted -zxf dummy.tgz
$ du -sh dummy extracted/dummy
0       dummy
52K     extracted/dummy

$ tar -S -zcf dummy.tgz dummy
$ tar -C extracted -zxf dummy.tgz
$ du -sh dummy extracted/dummy
0       dummy
0       extracted/dummy

You can also "re-sparse" a file afterwards with cp --sparse=always:

$ dd if=/dev/zero of=junk count=100
...
$ du -sh junk
52K     junk
$ cp --sparse=always junk junk.sparse && mv junk.sparse junk
$ du -sh junk
0       junk

@mosvy points out that your files were probably sparse. Re-doing the archive + extract with tar --sparse works, or you can make existing files in the filesystem sparse again using
fallocate -d (from util-linux) to punch holes in in-place.

for f in **/*some*pattern*;do
    fallocate --dig-holes "$f"
done

The man page describes this option as

You can think of this option as doing a cp --sparse and then renaming the destination file to the original, without the need for extra disk space.

---

Linux supports the fallocate(2) system call which allows cool stuff like this, including closing up or expanding page-sized holes in a file to shorten or grow a file, instead of just turning a range into a hole. It depends on the underlying FS to support each of the various fallocate features separately, and of course sparse files / extents in general.

It also lets you preallocate unwritten extents (like hole but with space reserved on disk), e.g. before a torrent download to avoid fragmentation. That's where the "allocate" in the name comes from.

Other kernels that util-linux can run under may support some or all of this functionality, IDK. If it doesn't work, cp --sparse and rename should work; sparse files in general (seek instead of writing zeros) are well-established and widespread in Unix, dating back much much farther than preallocated extents, punching holes, or especially expanding or collapsing holes between existing data.