Configuring Units28 3ware 9000 Series Serial ATA RAID Controller Installation GuideNote: This section describes how to configure yourRAID arrays as part of the installation process. Forcomplete information about using 3ware BIOS Manager(3BM), including how to use it to change existingconfigurations, and for information about how to defineand change the configuration using 3ware Disk Manager(3DM 2), see the 3ware 9000 Series Serial ATA RAIDController User Guide.Note: You must attach drives before you can configureRAID arrays. If no drives are attached to the 3wareRAID controller, the 3ware BIOS will not be installed.Understanding RAID Concepts andLevelsThe following concepts are important to understand when selectingthe appropriate RAID level for a system: Arrays and Units. In the storage industry, the term “array” isused to describe two or more disk drives that appear to theoperating system as a single unit. When you work with 3waresoftware, “unit” is the term used to refer to an array of disksthat is configured and managed through the 3ware software.Single-disk units can also be configured in the 3ware software. Mirroring. Mirrored arrays write data to paired drivessimultaneously. If one drive fails, the data is preserved on thepaired drive. Mirroring provides data protection throughredundancy. In addition, mirroring using a 3ware RAIDcontroller provides improved performance because 3ware’sTwinStor technology reads from both drives simultaneously. Striping. Striping across disks allows data to be written andaccessed on more than one drive, at the same time. Stripingcombines each drive’s capacity into one large volume. Striped
