I have a new client that is looking to create a system that has has two servers that is kept in a hot-failover configuration. We are looking at using the clustering howto with DRDB and Heartbeat, but have a question regarding analog line cards. How should this be handled so the cards don't interfere (burn out) each other. Because of the environment, manually moving the connections is not an option.

markh

Try the Xorcom fail-over stuff (two usb ports) , they come in many flavors.

But also in the absence of dahdi being loaded (add it to the haresources file and let heartbeat manage loading and unloading it. ) the FXO's which are "current sinks" will be in a high impedance state and thus not sink any current from the circuit (at least real ones from Digium Rhino or Sangoma, I can't speak for the inferior "knock-offs" ) and not cause any interaction with other bridged and operational FXO's. The same actually applies to FXS's, they are current sources but equally go high impedance in the absence of the driver being loaded.

Analog telephony is based on "current loops", well designed ones really can't "burn out" anything, these designs are nearly 150 years old, in the absence of lightning or a gamma ray burst from alpha centuri, you are probably safe, 600 ohms at 48 volts run through ohms law will hopefully alleviate your worries.