Wiki

RAID configurations

Configuration

Minimum number
of drives

Usable space

Read Performance

Write Performance

Cost/MB

Single drive failure
data loss probability

Dual drive failure
data loss probability

RAID 0 (striping only, no redundancy)

2

all drives

{*} {*} {*}

{*} {*} {*}

x1

100% [note 1]

100%

RAID 1

2

1/2 x number of drives

{*} {*} {o}

{*} {*} {o}

x2

0%

100%

RAID 1

3

1/3 x number of drives

{*} {*} {*}

{*} {*} {o}

x3

0%

0%

RAID 1E (1 Enhanced)

3

1/2 x number of drives

{*} {*} {o}

{*} {*} {o}

x2

0%

100%

RAID 5

3

number of drives minus 1

{*} {*} {*}

{*} {o} {o}

x1.5

0%

100%

RAID 5

4

number of drives minus 1

{*} {*} {*}

{*} {o} {o}

x1.33

0%

100%

RAID 5EE (5 + distributed hot spare)

4

number of drives minus 2

{*} {*} {*}

{*} {o} {o}

x2

0%

0% [note 2]

RAID 50 (5 + striping)

6

number of drives minus 2

{*} {*} {*}

{*} {o} {o}

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

{*} {*} {o}

{*} {o} {o}

x2

0%

0%

RAID 60 (dual striped RAID6)

8

number of drives minus 4

{*} {*} {o}

{*} {o} {o}

x1.33

0%

0%

Notes

  1. 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.

  2. 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.
  3. 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.
  4. Write intensive applications - RAID 1 is best
  5. Write intensive applications with very large storage requirements - RAID 10 is best
  6. Read intensive applications - RAID 5 is best.
  7. RAID 5 is not recommend for database servers with any significant volume of write activities.
  8. 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

Wiki: dedicated/RAID_configurations (last edited 2010-02-04 09:00:46 by MichaelChapman)