Lesson4.Setting Up Your Storage

Lesson 4. Setting Up Your Storage

The Apple Xserve RAID (redundant array of independent disks) is a group of hard drives that appears to the host Power Mac as a single high-speed storage unit. RAID systems enable you to increase storage capacity and get the performance, reliability, and data protection needed for video production, which is not possible from a single hard drive. RAID drives inside the array operate simultaneously, increasing overall throughput. Some or all of the following techniques are used in RAID technology:

• RAID level 0: Striping data across multiple drives for storage performance

• RAID level 1: Mirroring for redundancy

• RAID level 3 and 5: Parity for data protection (plus others)

Most RAID configurations combine these techniques to provide a balance of protection and performance. Striping divides a logical drive into data blocks, or stripes, that are distributed across an array of physical drives. Striping a set of disks improves storage performance because each drive operates concurrently. However, striping alone, known as RAID level 0, offers no data protection. Mirroring involves writing identical copies of all data to a pair of physical drives. This results in very high data reliability; if one drive fails, the data is still available on the remaining drive. However, it also results in a storage efficiency of only 50 percent, because two physical drives are required to achieve a single drive's capacity. Mirroring alone is known as RAID level 1. Parity provides data protection without requiring a complete duplication of the drive contents. In the event of drive failure, parity information can be used with data on the surviving drives to reconstruct the contents of a failed drive. Parity data can be stored on a dedicated drive, as in RAID 3, or distributed across an array of drives, as in RAID 5. Parity provides much greater storage efficiency than mirroringup to 85 percent for a set of seven drives.