76 Hog 4 Operations Manual
Understanding Multi-Server Fail over Behavior
Below are some specific rules and examples that describe how the Hog 4 OS works when
setup in a Multi-Console / Multi-Server environment:
1. The server that initially launches a show is the active server. Other servers that join the
show are backup servers. The active server replicates it's copy of the show to all
backup servers as they join the show, replacing any existing copy of the show on the
backup servers.
2. If all servers stay connected to the network and remain visible to each other, then all
servers will have the same copy of the show. New data created on any console will
immediately replicate to all servers.
3. If any server logs off, then the remaining servers will continue to store the show and
can replicate the show to new consoles that log on. As long as at least one server is
always available, then consoles can log off and log on at will.
4. If any server logs off the show and later rejoins, it will always rejoin as a backup server,
and the active server will replicate it's current copy of the show to the backup.
5. If all servers log off at the same time then any server can initially launch the show,
since all servers will have the same data. However, the last server to shut down will
also clean up the database, so it's preferable that this be the initial server when starting
up next time. So it's preferable to designate a single console to store the "master" copy
of the show, and ensure it's always the first server to start and the last server to shut
down.
6. If some servers log off, then new data continues to be replicated to the remaining
servers. If all servers then log off, some consoles will have newer data (the consoles
that remained logged in), and some will have older data (the consoles that logged off
early). Launching a server using an older copy of the show makes that the active
server, and any servers that then join will be backup servers and the old data will be
replicated to them. That includes servers that may have had a newer copy of the show.
So here is one way that new show data may be lost, replaced with old show data from a
console that never saw it.
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