a.) Multiple databases under a single binary and host require more resources and could lead to contention for these resources, which may pique performance problems, if you don't have enough resources on the host to distribute evenly or share.
b.) Multiple databases, under single binary and host translate to a single point of failure. If you need to apply a patch, for example, or there is a problem with the binary.
c.) Multiple databases with multiple binaries under a single or multiple host would require more planning, administration, maintenance, resources etc and could lead to performance problems if you don't have enough resources to distribute evenly. However, this guide against single point of failure in case you have problem with a single binary or host.
d.) Multiple schemas in a single database, obviously under a single binary and host, makes management and administration tasks relatively cheaper and easier and would accord the database or schemas with enough resources which may translate to performance improvements.
e.) Multiple schemas in a single database however translate to a single point of failure, that is, if a schema in the database has problems that means the rest of the schemas, by default, would be affected. To perform restore and recovery on a single schema, would most likely affect the rest of the schemas depending on the type of backup you have.
f.) Multiple schemas in a single database could save you on Oracle licences and also makes it easier to have a RAC-enabled environment which will translate your application to Higher Availability.
All in all, choosing the best method can't be made in silo, and will require bringing the architecture, the application(s), project scope, budget and business needs into the full picture.
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