The data storage layer stores persistent data in several places within Jira. Most business data, such as projects and issues, are stored in a relational database. Content such as uploaded attachments and search indexes are stored in the filesystem in the JIRA_HOME directory, which we will talk about in the next section. The underlying relational database that's used is transparent to users, and you can migrate from one database to another with ease, as referenced at https://confluence.atlassian.com/adminjiraserver/switching-databases-938846867.html.