Q: How Recursively Sub Directory Can Be Created ?

The structore holding the html-ized article is as follows:

200201/msg\d+.html

One sub-directory by default.

Consider directory listing. "ls" returns 1000 files soon, but 10000 files a little slowly.

To accelerate listing, we should use sub-directory structure. For example, each sub-directory holds 1000 files. The structure such as "spool/sub/file" holds 10^6 ( million ) files and listing of it is fast.

It must be enough to assume that 1 million articles for one ML.