This section provides an overview of each RAID level. Use this information to select the best level of protection for your storage.
Note! In the RAID descriptions below the term drive segment (or simply segment) refers to a portion of a disk drive. Not all RAID levels are supported by all controllers.
A logical device with RAID 0 includes two or more disk drives and provides data striping, where data is distributed evenly across the disk drives in equal-sized sections. However, RAID 0 arrays do not maintain redundant data, so they offer no data protection.
Compared to an equal-sized group of independent disks, a RAID 0 array provides improved I/O performance.
Drive segment size is limited to the size of the smallest disk drive in the logical device. For instance, a logical device with two 250 GB disk drives and two 400 GB disk drives can create a RAID 0 drive segment of 250 GB, for a total of 1000 GB for the volume, as shown in this figure.
A RAID 1 logical device is built from two disk drives, where one disk drive is a mirror of the other (the same data is stored on each disk drive). Compared to independent disk drives, RAID 1 logical devices provide improved performance, with twice the read rate and an equal write rate of single disks. However, capacity is only 50 percent of independent disk drives.
If the RAID 1 logical device is built from different-sized disk drives, drive segment size is the size of the smaller disk drive, as shown in this figure.
A RAID 1 Enhanced (RAID 1E) logical device—also referred to as a striped mirror—is similar to a RAID 1 logical device except that data is both mirrored and striped, and more disk drives can be included. A RAID 1E logical device can be built from three or more disk drives.
In this figure, the large bold numbers represent the striped data, and the smaller, non-bold numbers represent the mirrored data stripes.
A RAID 10 logical drive is built from two or more equal-sized RAID 1 logical drives. Data in a RAID 10 logical drive is both striped and mirrored. Mirroring provides data protection, and striping improves performance.
Drive segment size is limited to the size of the smallest disk drive in the logical drive. For instance, a logical drive with two 250 GB disk drives and two 400 GB disk drives can create two mirrored drive segments of 250 GB, for a total of 500 GB for the logical drive, as shown in this figure.
A RAID 5 logical device is built from a minimum of three disk drives, and uses data striping and parity data to provide redundancy. Parity data provides data protection, and striping improves performance.
Parity data is an error-correcting redundancy that’s used to re-create data if a disk drive fails. In RAID 5 logical devices, parity data is striped evenly across the disk drives with the stored data.
Drive segment size is limited to the size of the smallest disk drive in the logical drive. For instance, a logical drive with two 250 GB disk drives and two 400 GB disk drives can contain 750 GB of stored data and 250 GB of parity data, as shown in this figure (where P represents parity).
A RAID 5EE logical device—also referred to as hot space—is similar to a RAID 5 logical device except that it includes a distributed spare drive and must be built from a minimum of four disk drives.
Unlike a hot spare, a distributed spare is striped evenly across the disk drives with the stored data and parity data, and can’t be shared with other logical devices. A distributed spare improves the speed at which the logical device is rebuilt following a disk drive failure.
A RAID 5EE logical device protects your data and increases read and write speeds. However, capacity is reduced by two disk drives’ worth of space, which is for parity data and spare data.
In this example, S represents the distributed spare, P represents the distributed parity data.
A RAID 50 logical device is built from at least six disk drives configured as two or more RAID 5 logical devices, and stripes stored data and parity data across all disk drives in both RAID 5 logical devices.
The parity data provides data protection, and striping improves performance. RAID 50 logical devices also provide high data transfer speeds.
Drive segment size is limited to the size of the smallest disk drive in the logical device. For example, three 250 GB disk drives and three 400 GB disk drives comprise two equal-sized RAID 5 logical devices with 500 GB of stored data and 250 GB of parity data. The RAID 50 logical device can therefore contain 1000 GB (2 x 500 GB) of stored data and 500 GB of parity data.
In this example, P represents the distributed parity data.
A RAID 6 logical device—also referred to as dual drive failure protection—is similar to a RAID 5 logical device because it uses data striping and parity data to provide redundancy. However, RAID 6 logical devices include two independent sets of parity data instead of one. Both sets of parity data are striped separately across all disk drives in the logical device.
RAID 6 logical devices provide extra protection for your data because they can recover from two simultaneous disk drive failures. However, the extra parity calculation slows performance (compared to RAID 5 logical devices).
RAID 6 logical devices must be built from at least four disk drives. Maximum stripe size depends on the number of disk drives in the logical device.
Similar to a RAID 50 logical device, a RAID 60 logical device—also referred to as dual drive failure protection—is built from at least eight disk drives configured as two or more RAID 6 logical devices, and stripes stored data and two sets of parity data across all disk drives in both RAID 6 logical devices.
Two sets of parity data provide enhanced data protection, and striping improves performance. RAID 60 logical devices also provide high data transfer speeds.