Re: What is an instance?

This is a lot easier to explain with a white board... You can think of an instance (server) as a set of memory structures and system processes which access database files. With Informix, you can have several databases within an instance and each database can have tablespaces across all of the dbspaces associated with that instance. You can have multiple database servers on the same physical computer (hence the ONCONFIG SERVERNUM parameter), and these are all physically separate; different memory and physical disk resources. The only thing they can share are the INFORMIXDIR files (sqlhosts, bin files, ...). When you start ontape, it reads the current INFORMIXSERVER / ONCONFIG variables and then can determine where the server is (in memory) that it has to backup. > The books I have read do not help me understand what an instance is. If I have > one rootdbs, and 2 dbspaces with data, is there 1 instance? Yes. You can create multiple databases in this instance, but it will never be more than a single instance. Check the Admin. Guide for info about running several instances on the same machine. > Also, if I have a live database in 1 dbspace and a train database in another > dbspase, will ontape archive them both? If so, will I be able to restore in the > future to only 1 database, say train, and not overwrite live? Both of these databases are in the same server and since ontape is associated with a database server, it will backup / log all activity / databases on that server. You can have one or hundreds of databases in the server, ontape does not care. SC