Use Of Shared Storage In High Availability Arrays?

urbanjunkie asks: "I want to ensure my web site/database farm/whatever is as available as possible, so I checked out many HA (High Availability) packages for Linux. It seems that they -all- seem to want me to use shared storage. I don't want to use shared storage since it moves the point of failure to the disk array. I know that the disk array can be RAIDed etc, but what about a fire, power loss and any of the other things that can go wrong? I'd prefer to have something that replicated changes made to one disk to another disk located in a separate PC that may well be in a location 100 metres away. Is there anything open sourced that can do this?"