Wikipedia: History of RAID

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Changed: 5c5

There are 6 levels: RAID 0 to RAID 5. There can also be combinations of RAID levels.

There are 6 official levels: RAID 0 to RAID 5. There can also be combinations of RAID levels.

Added: 10a11,22

Hardware vs. Software

Any of the RAID levels listed below can be implemented in hardware or software.

With a software implementation, the operating system itself manages the disks of the array through the normal drive controller (IDE, SCSI, FC). This option can be slow, but it does not require the purchase of extra hardware.

A hardware implementation of RAID requires (at a minimum) a special-purpose RAID controller card. This controller handles the management of the disks, and performs parity calculations (needed for RAID 4, 5). This option tends to provide better performance, and makes operating system support easier.

Hardware implementations also typically support [hot swap]?, allowing failed drives to be replaced while the system is running.

Added: 37a50

Changed: 53,55c66

Highest disk overhead of all RAID types (100%) inefficient. Typically the RAID function is done by system software, loading the CPU/Server? and possibly degrading throughput at high activity levels. Hardware implementation is strongly recommended.

May not support hot swap of failed disk when implemented in "software".

Highest disk overhead of all RAID types (100%) inefficient.

Added: 61a73,77

RAID 3

RAID level 3 is rarely implemented.

	Revision 7 . . November 26, 2001 7:46 am by The ansible [added section on hardware vs. software RAID]
	Revision 6 . . November 24, 2001 1:43 am by Damian Yerrick [FS clusters offset raid 5 disadvantage]
	Revision 5 . . (edit) November 2, 2001 6:14 pm by Ramesh