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RAID 6—Striped Set With Dual Distributed Parity

While RAID 5 accommodates the loss of any one drive in the array, RAID 6 can allow for the failure of two drives and still function. This redundancy is achieved by writing the same parity information to two different disks.

Note There are many and varied RAID configurations that are simply combinations of the standard RAID levels. Nested RAID solutions are becoming increasingly common with larger arrays of disks that require a high degree of both reliability and speed. Some common nested RAID levels include RAID 0 + 1, 1 + 0, 5 + 0, 6 + 0, and (1 + 0) + 0, which are also commonly written as RAID 01, 10, 50, 60, and 100, respectively.

RAID 1 + 0 or RAID 10

RAID 1 + 0 or RAID 10 is an example of what is known as nested RAID or multi-RAID, which simply means that one standard RAID level is encapsulated within another. With RAID 10, which is also commonly written as RAID 1 + 0 to explicitly indicate the nesting, the configuration is a striped set of mirrors.

System Redundancy

Though redundancy and resiliency of data, provided by RAID and backup solutions, are important, further consideration needs to be given to the systems themselves that provide access to this redundant data.

Redundant Hardware

Many systems can provide internal hardware redundancy of components that are extremely prone to failure. The most common example of this in-built redundancy is systems or devices that have redundant onboard power in the event of a power supply failure. In addition to redundant power, it is also common to find redundant network interface cards (NICs), as well as redundant disk controllers. Sometimes systems simply have field replaceable modular versions of commonly failing components. Though physically replacing a power supply might increase downtime, having an inventory of spare modules to service the entire datacenter’s servers would be less expensive than having all servers configured with an installed redundant power supply.