DHCP

Put the scope on only 1 DHCP server, but this defeats the purpose of having a fall-back position in the even of a server outage.

You usually configure the router to specify which DHCP server to use and which scope to apply to each subnet.

As for backups, you can set up a 2nd server but not enable or authorise it and just regularly copy the DHCP database across regularly to backup server in case of disaster.

Guess I was not explaining our situation clearly. We have 2 floors connected to the same switch, but users on each floor require different settings to be recvd from the DHCP srvr. Now users get a response from either srvr which makes some of their applications inaccessible. We have considered increasing lease time to abt 300days. We wanted to set up the client pc's so that the client waits for a response from the specific DHCP srvr and reject any other responses.

You could setup Vlans on your switches, depends if they are capable the you let the One DHCP run on Vlan 1 and the Other on Vlan 2.

You should only need 1 DHCP server in any domain. But if you insist on running 2 servers then you will have to create reservations on each server for each device on that floor. To create a reservation you will need the MAC address of each device, you then reserve an IP address by associating it to the MAC addr of the device.