RAID
RAID is an acronym which stands for Redundant Array of Inexpensive Disks or Redundant Array of Independent Disks. The purpose of setting up a RAID array is to increase either hard drive performance or data reliability (or, in some implementations, both). This is achieved by getting the computer to treat more than one hard drive as though it were a single device.
RAID can be implemented through a hardware-based or software-based solution. A hardware-based solution is more expensive but provides better performance. There are three commonly used types of RAID: RAID 0, RAID 1, and RAID 5. You can also combine different types of RAID arrays, such as RAID 0+1 and RAID 1+0, which is called nesting.
RAID Levels
RAID 0, also known as disk striping, is not fault-tolerant. This method requires that you use no less than 2 and no more than 32 hard drives. Data saved to the drive is split up in to pieces and stored across the various drives of the array. This method of storage allows for greater speed, but if any of the drives fail, all of the data is lost.
RAID 1, also known as disk mirroring or disk duplexing, is fault-tolerant, but you lose 50% of your disk storage to gain redundancy. This method requires that you use no less than 2 and no more than 32 hard drives. Data saved to the drive is split up in to pieces and stored across half of the drives of the array while a duplicate copy of the same data is store in the other half.
RAID 5, also known as disk striping with parity, is fault-tolerant. This method requires that you use no less than 3 and no more than 32 hard drives. It has fast read/write speed, but not as fast as RAID 0. Parity information is stored on the drives so that, if one disk fails, the data lost can be reconstructed from the other disks, but performance will drop off when this occurs. You only lose 1 disk worth of storage to gain the fault-tolerance. If more than one disk fails before the data can be reconstructed, all of the data is lost.
Nesting
RAID 0+1 – You would create RAID 0 (stripe) sets and then mirror them (RAID 1). Doing this provides fault-tolerance and increased performance. Also, the data is available if one or more disks in a single set fails. However, data is lost if two disks in different mirrored sets fail. It requires an even number of disks (minimum of 4 disks) and you lose 50% of the disk space for fault-tolerance.
RAID 1+0 – You would create RAID 1 (mirror) sets and then stripe them (RAID 1). This provides better performance and fault-tolerance than RAID 0+1. Also, data is available if one or more disks in a single set fails or even if two disks in different sets fail. It requires an even number of disks (minimum of 4 disks) and you lose 50% of the disk space for fault-tolerance.
Related Material
YouTube video documenting the creation of a RAID array using 24 SSD hard drives:
Articles on RAID from Tom's Hardware website:
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