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Diagram of a RAID 1 setup. RAID 1 consists of an exact copy (or mirror) of a set of data on two or more disks; a classic RAID 1 mirrored pair contains two disks.This configuration offers no parity, striping, or spanning of disk space across multiple disks, since the data is mirrored on all disks belonging to the array, and the array can only be as big as the smallest member disk.
The first number in the numeric designation denotes the lowest RAID level in the "stack", while the rightmost one denotes the highest layered RAID level; for example, RAID 50 layers the data striping of RAID 0 on top of the distributed parity of RAID 5. Nested RAID levels include RAID 01, RAID 10, RAID 100, RAID 50 and RAID 60, which all ...
RAID (/ r eɪ d /; redundant array of inexpensive disks or redundant array of independent disks) [1] [2] is a data storage virtualization technology that combines multiple physical data storage components into one or more logical units for the purposes of data redundancy, performance improvement, or both.
Normally, RAID controllers can be fully configured through card BIOS before an operating system is booted, and after the operating system is booted, proprietary configuration utilities are available from the manufacturer of each controller, because the exact feature set of each controller may be specific to each manufacturer and product.
Under traditional RAID, an entire disk storage system of, say, 100 disks would be split into multiple arrays each of, say, 10 disks. By contrast, under declustered RAID, the entire storage system is used to make one array. Every data item is written twice, as in mirroring, but logically adjacent data and copies are spread arbitrarily.
The amount of data in one stride multiplied by the number of data disks in the array (i.e., stripe depth times stripe width, which in the geometrical analogy would yield an area) is sometimes called the stripe size or stripe width. [5] Wide striping occurs when chunks of data are spread across multiple arrays, possibly all the drives in the system.
A flawed RAID 5/6 also exists, but can result in data loss.) [10] For RAID 1, the devices must have complementary sizes. For example, a filesystem spanning two 500 GB devices and one 1 TB device could provide RAID1 for all data, while a filesystem spanning a 1 TB device and a single 500 GB device could only provide RAID1 for 500 GB of data.
In the case of a RAID 3 array of 12 drives, 11 drives participate in the XOR calculation shown above and yield a value that is then stored on the dedicated parity drive. Extensions and variations on the parity bit mechanism "double," "dual," or "diagonal" parity, are used in RAID-DP.