$hash = '123456789';
$fileName = "test.{$hash}.html";
the final directory structure will be like following.
te/st/.1/23/45/67/test.123456789.html
it simply breaks down the file name in to directories of two characters leaving the last 2 chars from the path test.123456789
To prevent too many files in one folder
error.
See https://docs.phalcon.io/4.0/en/cache#stream as well.