RAID configurations
Configuration |
Minimum number |
Usable space |
Read Performance |
Write Performance |
Cost/MB |
Single drive failure |
Dual drive failure |
RAID 0 (striping only, no redundancy) |
2 |
all drives |
|
|
x1 |
100% [note 1] |
100% |
RAID 1 |
2 |
1/2 x number of drives |
|
|
x2 |
0% |
100% |
RAID 1 |
3 |
1/3 x number of drives |
|
|
x3 |
0% |
0% |
RAID 1E (1 Enhanced) |
3 |
1/2 x number of drives |
|
|
x2 |
0% |
100% |
RAID 5 |
3 |
number of drives minus 1 |
|
|
x1.5 |
0% |
100% |
RAID 5 |
4 |
number of drives minus 1 |
|
|
x1.33 |
0% |
100% |
RAID 5EE (5 + distributed hot spare) |
4 |
number of drives minus 2 |
|
|
x2 |
0% |
0% [note 2] |
RAID 50 (5 + striping) |
6 |
number of drives minus 2 |
|
|
x1.5 |
0% |
40% |
RAID 10 |
4 |
1/2 x number of drives |
|
|
x2 |
0% |
33% |
RAID 6 (dual parity) |
4 |
number of drives minus 2 |
|
|
x2 |
0% |
0% |
RAID 60 (dual striped RAID6) |
8 |
number of drives minus 4 |
|
|
x1.33 |
0% |
0% |
Notes
RAID 0 is more dangerous than a single drive, as the loss of any drive will result in the loss of the data on all drives.
- A RAID 5EE array is at risk of data loss from a second failed drive if the array has not completely rebuilt at the time of the second drive loss. Given the tendency of disks from the same batch to fail at the same time, and the added stress that a rebuild puts on all the disks in an array, the risk of a second disk failure is a real one.
- In all of the above configurations, if capacity in the chassis permits, additional drives can be added to provide increased redundancy in the case of failure. This does not improve performance however.
- Write intensive applications - RAID 1 is best
- Write intensive applications with very large storage requirements - RAID 10 is best
- Read intensive applications - RAID 5 is best.
- RAID 5 is not recommend for database servers with any significant volume of write activities.
For more information see the Wikipedia RAID article, and Non standard RAID levels
Sample drive configurations
No. Drives |
Drive Capacity |
RAID Configuration |
Total Capacity |
Drive options |
SATA |
||||
2 |
80 |
1 |
80 |
- |
3 |
80 |
5 |
160 |
- |
4 |
80 |
5 |
240 |
- |
2 |
160 |
1 |
160 |
- |
3 |
160 |
5 |
320 |
- |
4 |
160 |
5 |
480 |
- |
2 |
300 |
1 |
300 |
- |
3 |
300 |
5 |
600 |
- |
4 |
300 |
5 |
900 |
- |
3 |
500 |
5 |
1,000 |
- |
4 |
500 |
5 |
1,500 |
- |
2 |
750 |
1 |
750 |
- |
3 |
750 |
5 |
1,500 |
- |
4 |
750 |
5 |
2,250 |
- |
SCSI/SAS |
||||
2 |
73 |
1 |
73 |
SAS 15k, SCSI 10/15k |
3 |
73 |
5 |
146 |
SAS 15k, SCSI 10/15k |
4 |
73 |
5 |
219 |
SAS 15k, SCSI 10/15k |
2 |
143 |
1 |
143 |
SAS 15k, SCSI 10/15k |
3 |
143 |
5 |
286 |
SAS 15k, SCSI 10/15k |
4 |
143 |
5 |
429 |
SAS 15k, SCSI 10/15k |
2 |
300 |
1 |
300 |
SAS 15k, SCSI 10/15k |
3 |
300 |
5 |
600 |
SAS 15k, SCSI 10/15k |
4 |
300 |
5 |
900 |
SAS 15k, SCSI 10/15k |