Understanding RAID Concepts and Levelswww.3ware.com 5Available RAID ConfigurationsRAID is a method of combining several hard drives into one unit. It offersfault tolerance and higher throughput levels than a single hard drive or groupof independent hard drives. RAID levels 0, 1, 10 and 5 are the most popular.AMCC's 3ware controllers support RAID 0, 1, 5, 6, 10, 50, JBOD and SingleDisk. The information below provides a more in-depth explanation of thedifferent RAID levels.For how to configure RAID units, see “Configuring a New Unit” on page 96.RAID 0RAID 0 provides improved performance, but no fault tolerance. Since thedata is striped across more than one disk, RAID 0 disk arrays achieve hightransfer rates because they can read and write data on more than one drivesimultaneously. The stripe size is configurable during unit creation. RAID 0requires a minimum of two drives.When drives are configured in a striped disk array (see Figure 2), large filesare distributed across the multiple disks using RAID 0 techniques.Striped disk arrays give exceptional performance, particularly for dataintensive applications such as video editing, computer-aided design andgeographical information systems.RAID 0 arrays are not fault tolerant. The loss of any drive results in the loss ofall the data in that array, and can even cause a system hang, depending onyour operating system. RAID 0 arrays are not recommended for highavailability systems unless additional precautions are taken to prevent systemhangs and data loss.Figure 2. RAID 0 Configuration ExampleRAID 1RAID 1 provides fault tolerance and a speed advantage over non-RAID disks.RAID 1 is also known as a mirrored array. Mirroring is done on pairs ofdrives. Mirrored disk arrays write the same data to two different drives usingRAID 1 algorithms (see Figure 3). This gives your system fault tolerance bypreserving the data on one drive if the other drive fails. Fault tolerance is abasic requirement for critical systems like web and database servers.
