Dustin Snell [Network Automation] wrote: > > I know there is clustercats for ColdFusion but we want to do the database > server first. Everything I am reading says you need at least *three* > machines to do a simple mirror with SQL Server, is this true??
Depends on which definition of mirroring / clustering / replication / failover you use and whether the purpose is reduncancy or performance. For resilient eager multimaster replication you would need at least 3 systems so that as long as 2 systems can agree with eachother they have a quorum and can proceed. If you have only 2 systems and they lose their connection they can each get conflicting updates and they have no way to determine which one gets precedent, effectively deadlocking both systems. > We would like > to have two machines, machine A and Machine B. Machine B stays in synch with > A and only goes live if Machine A is out of service. Why would this need and > more than two machines? This is typically called a hot standby configuration. If it is implemented with a shared disk array you need only 2 systems, if you can afford to potentially loose one or a few transactions you can implement it with 2 shared-nothing systems. Jochem ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| Discover CFTicket - The leading ColdFusion Help Desk and Trouble Ticket application http://www.houseoffusion.com/banners/view.cfm?bannerid=48 Message: http://www.houseoffusion.com/lists.cfm/link=i:4:194579 Archives: http://www.houseoffusion.com/cf_lists/threads.cfm/4 Subscription: http://www.houseoffusion.com/lists.cfm/link=s:4 Unsubscribe: http://www.houseoffusion.com/cf_lists/unsubscribe.cfm?user=89.70.4 Donations & Support: http://www.houseoffusion.com/tiny.cfm/54
