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Software RAID

Software RAID definition

Software RAID is a method of grouping multiple hard drives into one unit (called an array) using software rather than hardware. It improves speed, storage, and data safety.

See also: NAS, fault tolerance, data redundancy, data center storage

History of software RAID

Software RAID originated in the 1980s alongside its hardware-based counterpart. As computers improved, software RAID turned out to be a cheaper and more flexible option than hardware solutions. It allowed users with basic hard drives to achieve RAID-like benefits without extra equipment.

Software RAID levels

Software RAID levels describe the different ways to distribute data across multiple drives. Here are the common levels of software RAID:

  • RAID 0 (striping). Data is split between drives in chunks. This boosts speed since several disks can be read or written to at the same time, but it offers no backup. If one drive fails, all data in the array is lost.
  • RAID 1 (mirroring). Data is duplicated across two drives. This provides backup because if one drive fails, the other still contains all the data. However, it doesn't offer a storage gain since both drives hold the same data.
  • RAID 5 (distributed parity). Data and parity (error-checking) information are spread across three or more drives. If one drive fails, its data can be reconstructed from the remaining data and parity information. This provides a balance between performance, capacity, and backup.
  • RAID 6 (double parity). It’s like RAID 5 but uses two parity blocks instead of one. This means the system can handle the failure of two drives at once.
  • RAID 10 (or 1+0). This level mixes RAID 1 and RAID 0. It involves striping data (RAID 0) across mirrored sets (RAID 1) of drives. It requires at least four drives and provides both performance and backup benefits.
  • RAID 50 (5+0). This is a combination of RAID 5 and RAID 0, where data is striped (RAID 0) across multiple RAID 5 arrays. It offers both speed and data safety.
  • RAID 60 (6+0). It combines RAID 6 and RAID 0, where data is striped (RAID 0) across multiple RAID 6 arrays. Like RAID 50, it offers performance enhancements along with even greater data safety due to the double parity of RAID 6.

Other RAID levels also exist, but they're less common in modern systems. The listed levels provide more efficient or flexible solutions for the needs of most users.