RAID Levels

RAID 4

So you want to work as a Storage Engineer, With SANs and NAS, then you should have good working knowledge of some basic terms in storage and backup. I'm talking about RAID levels, which you must understand. RAID which stands for redundant array of independent disks is the most widely used data protection technology which is used today and multiple disks work as part of a set to provide protection against HDD failures. Striping, Mirroring & Parity are the three basics of RAID levels, which we are going to discuss.

RAID Level 0
RAID 0 (Also known as a stripe set or striped volume) splits ("stripes") data evenly across two or more disks, without parity information, redundancy, or fault tolerance. Since RAID 0 provides no fault tolerance or redundancy, the failure of one drive will cause the entire array to fail; as a result of having data striped across all disks, the failure will result in total data loss. This configuration is typically implemented having speed as the intended goal. RAID 0 is normally used to increase performance, although it can also be used as a way to create a large logical volume out of two or more physical disks

​​RAID Level 1
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. This layout is useful when read performance or reliability is more important than write performance or the resulting data storage capacity. 

The array will continue to operate so long as at least one member drive is operational
Any read request can be serviced and handled by any drive in the array; thus, depending on the nature of I/O load, random read performance of a RAID 1 array may equal up to the sum of each member's performance, while the write performance remains at the level of a single disk. However, if disks with different speeds are used in a RAID 1 array, overall write performance is equal to the speed of the slowest disk.

​RAID Level 2
RAID 2, Which is rarely used in practice, stripes data at the bit (rather than block) level, and uses a Hamming code for error correction

​RAID Level 3
RAID 3, Which is rarely used in practice, consists of byte-level striping with a dedicated parity disk. One of the characteristics of RAID 3 is that it generally cannot service multiple requests simultaneously, which happens because any single block of data will, by definition, be spread across all members of the set and will reside in the same location

​RAID Level 4
RAID 4, Improves performance by striping data across many disks in blocks, and provides fault tolerance through a dedicated parity disk

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​RAID Level 5
One of the most popular RAID levels, RAID 5 stripes both data and parity information across three or more drives. It is similar to RAID 4 except that it exchanges the dedicated parity drive for a distributed parity algorithm, writing data and parity blocks across all the drives in the array. This removes the "bottleneck" that the dedicated parity drive represents, improving write performance slightly and allowing somewhat better parallelism in a multiple-transaction environment, though the overhead necessary in dealing with the parity continues to bog down writes. Fault tolerance is maintained by ensuring that the parity information for any given block of data is placed on a drive separate from those used to store the data itself. The performance of a RAID 5 array can be "adjusted" by trying different stripe sizes until one is found that is well-matched to the application being used.

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