Question about ext2/3 directory lookups

[Paul E Condon <pecondon@mesanetworks.net>]

Some time ago, ext2/3 became capable of organizing directories as
binary trees rather than linked lists. Is tree lookup standard in
Debian, or does one have to choose a special, non-default option when
creating the file system on a new partition?

I have a collection of about 1.5 million files, and need to decide
how to organize them. There won't be much activity. It will be an
archive, but linked list would probably be unacceptable for this
number of files even in an archive. (User would forget why he want
to look at the file before it finally opened ;-)

Advise welcome.
-- 
Paul E Condon           
pecondon@mesanetworks.net