Best way to delete users

We are running eDir 9.2.3 in a replica ring with 4 servers (2 servers running IDM 4.8.2 and 2 servers ldap-only, all 8 CPUs and 32GB ram). All servers have all partitions locally.

We need to remove around 2.5 million users from this tree, which is pretty much 98% of it. These are simple users with a few single-valued attributes only.

Our best approach was to do it using ldapdelete in batches of 50k users each. But our first experience showed that it took 3h for those 50k users to be deleted and synched, until the replica ring is healthy again with no 625 or 626 errors.

Any suggestions of better ways to do it?