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  A Quick Guide to RAID Levels  

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What is RAID?

RAID is an acronym for Redundant Array of Inexpensive (or Independent) Disks. A RAID array is a collection of drives which collectively act as a single storage system, which can tolerate the failure of a drive without losing data, and which can operate independently of each other.

What are the different RAID levels?

RAID 0

RAID 0 is not redundant, hence does not truly fit the "RAID" acronym. In Level 0, data is split across drives, resulting in higher data throughput. Since no redundant information is stored, performance is very good, but the failure of any disk in the array results in all data loss. This level is commonly referred to as striping.

RAID 1

RAID 1 is commonly referred to as mirroring with 2 hard drives. It provides redundancy by duplicating all data from one drive on another drive. The performance of a RAID 1 array is slightly better than a single drive, but if either drive fails, no data is lost. This is a good entry-level redundant system, since only two drives are required. However, since one drive is used to store a duplicate of the data, the cost per megabyte is high.

RAID 0/1 or 10

RAID 0/1 is a dual level array that utilises multiple RAID1 (mirrored) sets into a single array. Data is striped across all mirrored sets. As a comparison to RAID 5 where lower cost and fault tolerance is important, RAID 0/1 utilises several drives, in order to provide better performance. Each drive in the array is duplicated (mirrored). This eliminates the overhead and delay of parity. This level array offers high data transfer advantages of striped arrays and increased data accessibility (reads). System performance during a drive rebuild is also better than that of parity based arrays, since data does not need to be regenerated from parity information, but copied from the other mirrored drive.

RAID 5

RAID 5 is commonly referred to as striping with distributed parity. RAID 5 distributes parity among the drives. No single disk is devoted to parity. This can speed small writes in multiprocessing systems.

RAID 6

RAID 6 is essentially an extension of RAID 5 which allows for additional fault tolerance by using a second independent distributed parity scheme (dual parity). Data is striped on a block level across a set of drives, just like in RAID 5, and a second set of parity is calculated and written across all the drives; RAID 6 provides for an extremely high data fault tolerance and can sustain multiple simultaneous drive failures.

RAID 50

RAID 50 is a dual level array that utilises multiple RAID 5 sets into a single array. In RAID 50 array, a single hard drive failure can occur in each of the RAID 5 without any loss of data on the entire array. Keep in mind, as the number of hard drives increase in an array, so too, does the increased possibility of a single hard drive failure. Although there is an increased write performance in RAID 0/5, once a hard drive fails and reconstruction takes place, there is a noticeable decrease in performance, data/program access will be slower, and transfer speeds on the array will be effected.

 

Which RAID Level is right for you?

The right choice depends on the application. The RAID Levels below provide a brief summary and general uses. Please bear in mind that some RAID controllers do not support all RAID Levels listed below. Please check Technical Specifications for your RAID product for RAID Levels that are supported.

RAID Level Uses

RAID 0 (striping)

Any application which requires very high speed storage, but does not need redundancy.

RAID 1 (mirroring)

Applications which require redundancy with fast random writes; entry-level systems where only two drives are available. Small file servers are an example.

RAID 0/1 or 10 (mirroring and striping)

Dual level raid, combines multiple mirrored drives (RAID 1) with data striping (RAID 0) into a single array. Provides highest performance with data protection.

RAID 5 (distributed parity)

RAID 5 distributes parity among the drives. No single disk is devoted to parity. This can speed small writes in multiprocessing systems. Database servers are an example.

RAID 6 (dual distributed parity)

Level 6 provides for extremely high data fault tolerance and can sustain multiple drive failures. This is a perfect solution for mission critical applications

RAID 50

Dual level raid, combines multiple RAID 5 sets with data striping (RAID 0). Increased reliability and performance over standard RAID 5 that can stand a multiple drive failure; one hard drive per RAID 5 set.

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