I am using 3 virtual disks for a dbserver
is there any advantage of using a different sas or pvscsi contoller for each disk?
Normally I use an default scsi adapter for system OS and an paravirtual (pvscsi) for data. About your design, remember that maximum supported number of scsi controller are 4.
About the performance improvements, take a look at this blog post: Add multiple SCSI controllers to your VM to improve performance - Yellow Bricks