
E-6 Understanding 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 = 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 
If you store 
