3Ware 9550SXU-12 User Guide - Page 17

Understanding RAID Concepts and Levels In addition: • JavaScript must be enabled • Cookies must be enabled • For best viewing, screen resolution should be 1024 x 768 or greater, with 16-bit color or greater. For a complete listing of features and system requirements, refer to the 3ware SATA RAID Controller datasheets, available from the website at http:// www.3ware.com/products. Understanding RAID Concepts and Levels 3ware RAID controllers use RAID (Redundant Array of Inexpensive Disks) to increase your storage system's performance and provide fault tolerance (protection against data loss). This section organizes information about RAID concepts and configuration levels into the following topics: • "RAID Concepts" on page 5 • "Available RAID Configurations" on page 6 • "Determining What RAID Level to Use" on page 12 RAID Concepts The following concepts are important to understand when working with a RAID controller: • Arrays and Units. In the storage industry, the term "array" is used to describe two or more disk drives that appear to the operating system as a single unit. When working with a 3ware RAID controller, "unit" is the term used to refer to an array of disks that is configured and managed through the 3ware software. Single-disk units can also be configured in the 3ware software. • Mirroring. Mirrored arrays (RAID 1) write data to paired drives simultaneously. If one drive fails, the data is preserved on the paired drive. Mirroring provides data protection through redundancy. In addition, mirroring using a 3ware RAID controller provides improved performance because 3ware's TwinStor technology reads from both drives simultaneously. • Striping. Striping across disks allows data to be written and accessed on more than one drive, at the same time. Striping combines each drive's capacity into one large volume. Striped disk arrays (RAID 0) achieve highest transfer rates and performance at the expense of fault tolerance. www.3ware.com 5