Exporting each "deleted" user to a seperate LDIF file will make the server faster for regular searches, but it will be much slower if I want to check if a new username has ever been used (something which I want to avoid).One disadvantage of 1 is your database will grow and your searches will become slower. LDAP isn't really the place for archival data, if you want to preserve it export the LDIF for the user and archive that.
But if I understand correct, the search can be restricted to a certain subtree. So if I would archive in a different subtree, the frequent, regular searches will stay fast. And the not so frequent searches for all usernames that have ever been issued will be a bit slower, because it will also incorporate the archive subtree. But that archive subtree should still be much faster to query then hundreds of files, because they all live in a single file (or maybe just a few, depending on the db backend I guess).
Any thoughts on this? Isaac