Compaq 3200 manual Table E-1 RAID Level Characteristics, 6Understanding Drive Arrays

E-6Understanding Drive Arrays

Table E-1

RAID Level Characteristics

		Distributed Data		Data Guarding
		Guarding (RAID 5)		(RAID 4)
Usable Disk Space*		67% to 97%		67% to 97%
Disk Space Formula		(n-1)/n		(n-1)/n
(n = no. of drives)
Parity and		Parity distributed		Dedicated parity drive
Data Redundancy		over each drive
Minimum Number	3		3
of Drives
Comments		Tolerant of single		Tolerant of single
		drive failures. Higher		drive failures. Like
		performance than		RAID 5, RAID 4 uses
		RAID 4. Uses the		the least amount of
		least amount of		storage capacity for
		storage capacity for		fault tolerance.
		fault tolerance.

*All drives are the same capacity.

Mirroring (RAID 1)

50%

n/2

Duplicate data

2

Tolerant of multiple, simultaneous drive failures. Higher performance than RAID 4 or 5. RAID 1 uses the most storage capacity for fault tolerance, and requires an even number of drives.

No Fault Tolerance

(RAID 0)

100%

n

None

1

Best performance, but data is lost if any drive in the logical drive fails. RAID 0 uses no storage space for fault tolerance.

If you require a fault-tolerant system for critical data, Compaq recommends using RAID 5 for maximum storage space efficiency or RAID 1 if I/O performance is more important.

If you store non-critical data, and space and performance are both important, RAID 0 offers the best of both parameters. However, RAID 0 has no data protection and you will have to rely on backups in the event of hardware failure.