The specific procedures depend on the OS you are using. You have to consider three aspects of multidisk environements:
Disk Spanning: Allows you to create file systems that are too large for just one disk. If one disk fails, your file system fails.
Disk Striping: Improves performance by splitting data in small chunks over several disk - accessing the data in parrallel. If one disk fails, your file system fails.
Disk Mirroring: Duplexing / duplicating data on two (or more) disks.If one disk fails, the other one takes over.
In any of these schemas you want separate your data across different disks as well as different SCSI controllers and power supplies. If one SCSI controller fails, all disk on that controller fail. Ifthat controller contains both disks of a duplexed/mirror pair, the whole filesystem just failed.
Note that striping, spanning, and mirroring are not mutually exclusive. Just complex to plan out. Best solution - if resources (money) permit, would be hardware RAID: