Raid Explained

RAID stands for Redundant Array of Inexpensive (or sometimes "Independent") Disks.  RAID is a method of combining multiple hard disks in a single logical unit to offer high availability, performance or a combination of both.  This provides better resilience and performance than a single disk drive.

The benefits of RAID explained

• Provides real-time data recovery with uninterrupted access when a hard drive fails
• Increases system uptime and network availability
• Protects against data loss
• Multiple drives working in parallel increases system performance

Software RAID

Many operating systems provide functionality for implementing software based RAID systems.  The software RAID systems generate the RAID algorithms using the server CPU, this can severely limit the RAID performance.  Should a server fail the whole RAID system is lost.  Cheap to implement and only need a single SCSI controller.

Hardware RAID

All RAID algorithms are generated on the RAID controller board, thus freeing the server CPU.  Allows full benefits and data protection of RAID.  More robust and fault tolerant than software RAID.  Requires dedicated RAID controller to work.

RAID levels

Various RAID levels exist these are 0, 1, 2, 3, 4, 5, 6, 7, 10, & 0+1.  The levels of RAID protection varies with the RAID level selected RAID levels 0 & 1 are not technically RAID as they have no redundancy in the event of drive failure.  The most common RAID levels are shown below.  RAID levels 2, 4, 6, 7 & 0+1 are a combination of the other RAID levels shown.