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Understanding Redundant Array of Independent Disks (RAID)

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Understanding Redundant Array of Independent Disks (RAID)

Understanding Redundant Array of Independent Disks (RAID)



Redundant array of independent disks (RAID) is an internal or external storage technology that uses an array of hard disks and may be hardware- or software-based. Hardware RAID processing is done on the motherboard or a separate RAID card. Software-based RAID uses standard hard drive controllers and handles the RAID processing as a software layer that is either built into the OS or installed as an extra feature. RAID can be used in either Windows clients or servers.

    Note
RAID is sometimes also said to stand for redundant array of inexpensive disks.


Redundant Array of Independent Disks (RAID) is a multiple disk technology that either increases performance or allows for the automatic recovery of data from a failed hard drive by simply replacing the failed drive. There are several types of RAID that provide varying degrees of increased performance and/or fault tolerance. All of these techniques involve two or more hard drives operating together in some fashion.

Many different RAID levels exist, but the most commonly used are listed here:


  • RAID 0
  • RAID 1
  • RAID 5
  • RAID 0+1
  • RAID 1+0 or RAID 10


RAID 0 is also known as disk striping. Striping-File data is written simultaneously to multiple drives in the array, which act as a single larger drive. This is a form of RAID that doesn’t provide fault tolerance. Data is written across multiple drives, so one drive can be reading or writing while the next drive’s read/write head is moving. This makes for faster data access. However, if any one of the drives fails, all content is lost.

Understanding Redundant Array of Independent Disks (RAID) 7kZjKFD

RAID 1 is also known as disk mirroring. At RAID level 1, data is mirrored across two physical drives. If the RAID is implemented through hardware as opposed to software, users and applications see only a single logical drive at the OS level. When RAID is implemented through software, the OS sees the separate drives (in tools like Disk Management). RAID 1 provides fault tolerance by writing all data twice. RAID 1 is used to provide fault tolerance and quick failover. The negatives of RAID 1 include the loss of half of your storage space and the reduced performance of writes.

Understanding Redundant Array of Independent Disks (RAID) 8OtemTw

RAID 5 combines the benefits of both RAID 0 and RAID 1 and is also known as striping with parity. It uses a parity block distributed across all the drives in the array, in addition to striping the data across them. That way, if one drive fails, the parity information can be used to recover what was on the failed drive. A minimum of three drives is required (two or more for data and one for parity).

Understanding Redundant Array of Independent Disks (RAID) 1zpXb3A

RAID 0+1 combines the stripe sets with mirroring. RAID 0+1 means arrays implemented as RAID 1, whose elements are RAID 0 arrays. Such implementation has the benefits of RAID 0 speed and RAID 1 safety.

Understanding Redundant Array of Independent Disks (RAID) W7JcVW1

RAID 1+0, also known as RAID 10, is just the opposite of RAID 0+1. In this case, you will actually implement two or three mirror sets and then stripe data across those mirror sets. This provides fault tolerance as the foundation and performance as an added layer.

Understanding Redundant Array of Independent Disks (RAID) X0iXAj4

Understanding the various levels of RAID is important. If you determine that you need fault tolerance at the drive level, you will want to purchase a computer that provides this feature through hardware. Although you can implement RAID through software, the performance is not generally as high and it will take away processing power from the computer itself.


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