Installing an additional SSD or HDD into your computers optical bay is a common solution to upgrading your computer's storage. However, there can be some reading and writing issues when using a HDD in the optical bay therefore we do not recommend this configuration when using Serato applications.
Tip: If you are installing SSD to the optical drive please make sure you had SATA III (6Gbps) link speed chipset for the hard drive and the optical drive. If optical bay has SATA II (3Gbps) link speed chipset I would suggest you to move SSD drive to the hard drive slot and HDD to the optical drive.
Set the drive to "Never sleep" in the system preferences, or make sure the option to "put hard disks to sleep when possible" option is turned off, as if the drive goes to sleep you may see missing information from Serato applications.
If you are having issues using Serato applications and you are reading files from a drive that has been installed in the computers optical bay, try moving the data to your internal (system) drive and see if the problem continues.