10 Facts About RAID

Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the required level of redundancy and performance.

Each scheme, or RAID level, provides a different balance among the key goals: reliability, availability, performance, and capacity.

Term "RAID" was invented by David Patterson, Garth A Gibson, and Randy Katz at the University of California, Berkeley in 1987.

Many configurations other than the basic numbered RAID levels are possible, and many companies, organizations, and groups have created their own non-standard configurations, in many cases designed to meet the specialized needs of a small niche group.

Software RAID implementations are provided by many modern operating systems.

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Software-implemented RAID is not always compatible with the system's boot process, and it is generally impractical for desktop versions of Windows.

An advantage of this model over the pure software RAID is that—if using a redundancy mode—the boot drive is protected from failure during the boot process even before the operating system's drivers take over.

Frequently, a RAID controller is configured to "drop" a component drive if the drive has been unresponsive for eight seconds or so; this might cause the array controller to drop a good drive because that drive has not been given enough time to complete its internal error recovery procedure.

Consequently, using consumer-marketed drives with RAID can be risky, and so-called "enterprise class" drives limit this error recovery time to reduce risk.

The recovery of UREs involves remapping of affected underlying disk sectors, utilizing the drive's sector remapping pool; in case of UREs detected during background scrubbing, data redundancy provided by a fully operational RAID set allows the missing data to be reconstructed and rewritten to a remapped sector.