The indefinite article is used before singular non-specific nouns. The indefinite article is never used with plural and uncountable nouns.
Use a/an in the following cases:
- The first time you mention or refer to a noun.
- To mean one.
- To express quantity.
- To be able to orchestrate a standalone Veeam backup server, you must deploy a VAO agent on the server. [first mention]
- Create 2 backup jobs and a replication job. [one]
- Jobs with a lot / a large amount of metadata may increase the I/O requirements for the configuration database. [quantity]