How many files can I have safely in a subdirectory?

[Bruno Wolff III]

On Sun, Aug 30, 2009 at 09:00:12 -0700,
  z0diac <web2009 at zeroreality.com> wrote:
> 
> Someone recently told me to 'keep an eye on it' because certain setups can't
> hold more than X number of files in a single directory. Yet someone else
> said I could have over 1 trillion files in a single directory if the HDD was
> large enough...

When I have directories in the few million range doing mass changes gets
extremely slow.

Besides some the other other things mentioned, you need to worry about the
inode limit on the file system. The default now, is lower than it used to be.
This bit me once when I was moving a directory with lots of files to another
system with a similar size partition when i was expecting a similar inode
limit.