Data at rest = data persisted somewhere = anything written on your hard disk drive I am pretty sure your database stores things into /var/lib/mysql : this is w

Data at rest = data persisted somewhere = anything written on your hard disk drive I am pretty sure your database stores things into /var/lib/mysql : this is what would be encrypted (without support from the software) So, if you lose your SSD, nobody is able to read your database's content