RAID CONCEPTS

How to calculate the various sizes after RAID implementations?

RAID 0(Stripe Set)

RAID 0 splits data across drives, resulting in higher data throughput. The performance of this configuration is extremely high, but a loss of any drive in the array will result in data loss. This level is commonly referred to as striping.

Space efficiency = 1 (100%)

Fault tolerance = 0 disk(s) (none)

Total Disks X Size of DISK = Total Size

Size after implementation = Total Size X Space Efficiency

Suppose we are using 3 disks of 250GB size, after RAID 0 implementation we get the total size out to be:

3 * 250 = 750

750 * 1 = 750

Hence we get 750 as final disk size.

RAID 1(Mirror)

RAID 1 writes all data to two or more drives for 100% redundancy: if either drive fails, no data is lost. Compared to a single drive, RAID 1 tends to be faster on reads, slower on writes. This is a good entry-level redundant configuration. However, since an entire drive is a duplicate, the cost per megabyte is high. This is commonly referred to as mirroring.

Space efficiency = 0.5 (50%)

Fault tolerance = 1 disk(s)

Total Disks X Size of DISK = Total Size

Size after implementation = Total Size X Space Efficiency

Suppose we are using 3 disks of 250GB size, after RAID 1 implementation we get the total size out to be:

3 * 250 = 750

750 * 0.5 = 375

Hence we get 375 as final disk size.

RAID 5

RAID 5 stripes data at a block level across several drives, with parity equality distributed among the drives. The parity information allows recovery from the failure of any single drive. Write performance is rather quick, but because parity data must be skipped on each drive during reads, reads are slower. The low ratio of parity to data means low redundancy overhead.

Space efficiency = 0.666666666666667 (66.6666666666667%)

Fault tolerance = 1 disk(s)

Total Disks X Size of DISK = Total Size

Size after implementation = Total Size X Space Efficiency

Suppose we are using 3 disks of 250GB size, after RAID 5 implementation we get the total size out to be:

3 * 250 = 750

750 * 0.667 = 500

Hence we get 500 as final disk size.

RAID 6

RAID 6 is an upgrade from RAID 5: data is striped at a block level across several drives with double parity distributed among the drives. As in RAID 5, parity information allows recovery from the failure of any single drive. The double parity gives RAID 6 additional redundancy at the cost of lower write performance (read performance is the same), and redundancy overhead remains low.

Space efficiency = 0.5 (50%)

Fault tolerance = 2 disk(s)

Total Disks X Size of DISK = Total Size

Size after implementation = Total Size X Space Efficiency

Suppose we are using 4 disks of 250GB size, after RAID 6 implementation we get the total size out to be:

4 * 250 = 1000

1000 * 0.5 = 500

Hence we get 500 as final disk size.

RAID 10

RAID 10 is a striped (RAID 0) array whose segments are mirrored (RAID 1). RAID 10 is a popular configuration for environments where high performance and security are required. In terms of performance it is similar to RAID 0+1. However, it has superior fault tolerance and rebuild performance.

Space efficiency = 0.5 (50%)

Fault tolerance = 1 disk (min) to 2 disks (max)

Total Disks X Size of DISK = Total Size

Size after implementation = Total Size X Space Efficiency

Suppose we are using 4 disks of 250GB size, after RAID 10 implementation we get the total size out to be:

4 * 250 = 1000

1000 * 0.5 = 500

Hence we get 500 as final disk size.

RAID 50

RAID 50 combines RAID 5 parity and stripes it as in a RAID 0 configuration. Although high in cost and complexity, performance and fault tolerance are superior to RAID 5.

RAID 60

RAID 60 combines RAID 6 double parity and stripes it as in a RAID 0 configuration. Although high in cost and complexity, performance and fault tolerance are superior to RAID 6.

RAID 01

RAID 0+1 is a mirror (RAID 1) array whose segments are striped (RAID 0) arrays. This configuration combines the security of RAID 1 with an extra performance boost from the RAID 0 striping.

How to calculate the various sizes after RAID implementations?

RAID 0(Stripe Set)

RAID 0 splits data across drives, resulting in higher data throughput. The performance of this configuration is extremely high, but a loss of any drive in the array will result in data loss. This level is commonly referred to as striping.

Space efficiency = 1 (100%)

Fault tolerance = 0 disk(s) (none)

Total Disks X Size of DISK = Total Size

Size after implementation = Total Size X Space Efficiency

Suppose we are using 3 disks of 250GB size, after RAID 0 implementation we get the total size out to be:

3 * 250 = 750

750 * 1 = 750

Hence we get 750 as final disk size.

RAID 1(Mirror)

RAID 1 writes all data to two or more drives for 100% redundancy: if either drive fails, no data is lost. Compared to a single drive, RAID 1 tends to be faster on reads, slower on writes. This is a good entry-level redundant configuration. However, since an entire drive is a duplicate, the cost per megabyte is high. This is commonly referred to as mirroring.

Space efficiency = 0.5 (50%)

Fault tolerance = 1 disk(s)

Total Disks X Size of DISK = Total Size

Size after implementation = Total Size X Space Efficiency

Suppose we are using 3 disks of 250GB size, after RAID 1 implementation we get the total size out to be:

3 * 250 = 750

750 * 0.5 = 375

Hence we get 375 as final disk size.

RAID 5

RAID 5 stripes data at a block level across several drives, with parity equality distributed among the drives. The parity information allows recovery from the failure of any single drive. Write performance is rather quick, but because parity data must be skipped on each drive during reads, reads are slower. The low ratio of parity to data means low redundancy overhead.

Space efficiency = 0.666666666666667 (66.6666666666667%)

Fault tolerance = 1 disk(s)

Total Disks X Size of DISK = Total Size

Size after implementation = Total Size X Space Efficiency

Suppose we are using 3 disks of 250GB size, after RAID 5 implementation we get the total size out to be:

3 * 250 = 750

750 * 0.667 = 500

Hence we get 500 as final disk size.

RAID 6

RAID 6 is an upgrade from RAID 5: data is striped at a block level across several drives with double parity distributed among the drives. As in RAID 5, parity information allows recovery from the failure of any single drive. The double parity gives RAID 6 additional redundancy at the cost of lower write performance (read performance is the same), and redundancy overhead remains low.

Space efficiency = 0.5 (50%)

Fault tolerance = 2 disk(s)

Total Disks X Size of DISK = Total Size

Size after implementation = Total Size X Space Efficiency

Suppose we are using 4 disks of 250GB size, after RAID 6 implementation we get the total size out to be:

4 * 250 = 1000

1000 * 0.5 = 500

Hence we get 500 as final disk size.

RAID 10

RAID 10 is a striped (RAID 0) array whose segments are mirrored (RAID 1). RAID 10 is a popular configuration for environments where high performance and security are required. In terms of performance it is similar to RAID 0+1. However, it has superior fault tolerance and rebuild performance.

Space efficiency = 0.5 (50%)

Fault tolerance = 1 disk (min) to 2 disks (max)

Total Disks X Size of DISK = Total Size

Size after implementation = Total Size X Space Efficiency

Suppose we are using 4 disks of 250GB size, after RAID 10 implementation we get the total size out to be:

4 * 250 = 1000

1000 * 0.5 = 500

Hence we get 500 as final disk size.

RAID 50

RAID 50 combines RAID 5 parity and stripes it as in a RAID 0 configuration. Although high in cost and complexity, performance and fault tolerance are superior to RAID 5.

RAID 60

RAID 60 combines RAID 6 double parity and stripes it as in a RAID 0 configuration. Although high in cost and complexity, performance and fault tolerance are superior to RAID 6.

RAID 01

RAID 0+1 is a mirror (RAID 1) array whose segments are striped (RAID 0) arrays. This configuration combines the security of RAID 1 with an extra performance boost from the RAID 0 striping.

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