Why would addresses from a range not appear in the lease file

[Friesen, Don MTIC:EX]

>> My understanding was that with failover all IPs appear in the leases file, active or not.
>
>No. AIUI a lease does not appear in the file until the address has been used. Internally, every address in a range is present in the hash tables, but they aren't written out to disk until the lease info is "no longer blank".

   With failover... does primary record the leases assigned to the secondary in the leases file as vacant...  "backup", and those missing are assigned to the primary?  I just noticed that all the vacant leases in the dhcpd.leases file are tagged 'backup', which would be the delegation to the secondary peer, right?

lease 10.10.200.248 {
  starts 5 2016/04/22 19:40:29;
  tstp 5 2016/04/22 19:40:29;
  tsfp 5 2016/04/22 19:40:29;
  atsfp 5 2016/04/22 19:40:29;
  binding state backup;
}

Don Friesen