Generally, separating services roles improves the performance if you run them on different machines. Eg: database + frontend topology.
However, you won't notice any important performance improvement by altering the LAMP setup to have each role running on the same machine but using different disks.
We don't support this kind of customization from installing. Anyway, you could do some changes in your MySQL configuration file to point the data directory to a custom path. Please, take a look at this section in our documentation to do so.