Try this:
chmod ugo+x /mnt /mnt/storage /mnt/storage/cascornelissen
Probably some part of your path will not allow entry for your Apache user. Allowing entry to a directory means adding x
or execute permissions
to the directory.
Explanation
# create path a/b
mkdir -p a/b
ls a/b # this works
# now remove all permissions for a
chmod 000 a
ls a/b # ls: cannot access a/b: Permission denied
# but why, we should still have permission for b??
# Now, lets add x permission for a:
chmod ugo+x a
ls a/b # works again
ls a # ls: cannot open directory a: Permission denied
# So, we cannot list contents of a, but we can
# access a/b *through* a
So, execute permission
or x
for a directory means we can access the path below it, even if we cannot read the contents of the directory itself. In your case, Apache needs permission to "walk through" /mnt/storage/cascornelissen
even though it will not read any files until it reaches Muziek
.