Configure Redundant interface on ASA 5510 and above

Example  ASA redundant interface for Inside and DMZ interfaces. You need configure trunk  ports on switch.
Doesn’t support on ASA 5505. For ASA 5505 need use STP.

# interface Ethernet0/1
# no nameif
# no security-level
# no ip address

# interface Ethernet0/2
# no nameif
# no security-level
# no ip address

# interface Redundant1
# member-interface Ethernet0/1
# member-interface Ethernet0/2
# no nameif
# no security-level
# no ip address

# interface Redundant1.100
# vlan 100
# nameif Inside
# security-level 100
# ip address 10.10.100.1 255.255.255.0

# interface Redundant1.50
# vlan 50
# nameif DMZ
# security-level 50
# ip address 10.10.50.1 255.255.255.0

Rename or move nameif Inside, Outside on Cisco ASA

# copy running-config flash:/running-config.backup
# copy running-config tftp:

edit running-config on your PC with text editor compatible with unix text files

# copy tftp:  flash:/running-config.new
# copy flash:/running-config.new  startup-config
# reload

if you need return to old configuration

# copy flash:/running-config.backup  startup-config
# reload

P.S. was tested with ASA 8.3, works perfect