RAID Calculator

The RAID Calculator lets you map sectors between the RAID and its individual drives. For example if you want to know which sector on which individual member drive hosts sector 111 of a 3-drive backward RAID-5 with a block size of 128, you can find out like that:

In RAID Topology enter the RAID parameters: RAID-5, backward, 3 drives, start sector at 0, block size 128. Make sure the direction is "Global >> Local". Type "111" into the field for the Global sector. The right-hand side shows you the result: Global RAID sector 111 resides on local Drive1, sector 111.

You can reverse the direction and find out which global sector originates from a given local sector. Type "2" and "111" into the field for the Local sector. The left-hand side shows you the result, 239, which is to be expected as the first 128 sectors are on drive 1 and the next 111 on drive 2, resulting in 239.

Now try drive 3, sector 111:

As determined by the RAID topology, sector 111 on drive 3 is in a parity block and as such can not be translated into a global sector. The left-hand side signals this with "PARITY DRIVE".

Blocks, Stripes, and Cycles

Please note our terminology regarding "blocks", "stripes", and "cycles". The above defined RAID has the following characteristics:

In our example, one block consists of 128 sectors. One stripe are one block taken from each drive at the same position. Two of these blocks contain data, one is parity. One cycle is made of three stripes, which is the period it takes for the parity to make one full rotation.

Supported RAID types

The RAID Calculator supports the following RAID types:

RAID-0, striped array without redundancy
RAID-5, redundant array with 1 parity drive
RAID-6, redundant array with 2 parity drives
RAID-5 (HP), proprietary RAID scheme widely used by HP/Compaq RAID controllers

Supported Rotations

The directions of the rotation relates to the movement of the parity drive from one stripe to the next stripe within one cycle.

Backward (aka left-asymmetric):

Backward

Example: RAID-5, 3 drives, block size 128

Local drive
sector *) \

Drive 1

Drive 2

Drive 3

Cycle

Stripe

0-127

B1 **)

128-255

256-383

384-511

512-639

B10

640-767

B11

B12

*)	Sectors, cycles and stripes are 0-based, blocks and drives are 1-based
**)	Blocks B1, B2, B3, ... are data in the 1^st 128 global sectors (0-127), 2^nd 128 global sectors (128-255), 3^rd 128 global sectors (256-383), etc. P is parity for the blocks within the same stripe.

The name originates from the parity drive rotating backward (left) with each stripe until the start of a new cycle.

This is a very common rotation scheme used by many hardware RAID controllers.

Back. dyn (aka left-symmetric):

Backward dynamic

Example: RAID-5, 3 drives, block size 128

Local drive
sector *) \

Drive 1

Drive 2

Drive 3

Cycle

Stripe

0-127

B1 **)

128-255

256-383

384-511

512-639

B10

640-767

B11

B12

*)	Sectors, cycles and stripes are 0-based, blocks and drives are 1-based
**)	Blocks B1, B2, B3, ... are data in the 1^st 128 global sectors (0-127), 2^nd 128 global sectors (128-255), 3^rd 128 global sectors (256-383), etc. P is parity for the blocks within the same stripe.

As with the backward rotation, the backward dynamic rotation gets its name from the parity drive rotating backward (left) with each stripe until the start of a new cycle. It is very similar to backward, only stripe 1 arranges the blocks differently. The block to the right of parity P is the block with that stripe's lowest number, while in backward the lowest numbered block is always the first block. The blocks start to the right of parity P, incrementing by 1 with each block, rolling over to the first block and continuing until reaching parity P from the left side. Some people call this left-symmetric.

We call it backward dynamic because we first encountered this rotation scheme when examining Windows software RAID-5s that were created with dynamic disks partitioning. This rotation scheme is a very common and used by most software RAID-5s, under Windows and Linux.

Forward (aka right-asymmetric)

Forward

Example: RAID-5, 3 drives, block size 128

Local drive
sector *) \

Drive 1

Drive 2

Drive 3

Cycle

Stripe

0-127

B1 **)

128-255

256-383

384-511

512-639

B10

640-767

B11

B12

*)	Sectors, cycles and stripes are 0-based, blocks and drives are 1-based
**)	Blocks B1, B2, B3, ... are data in the 1^st 128 global sectors (0-127), 2^nd 128 global sectors (128-255), 3^rd 128 global sectors (256-383), etc. P is parity for the blocks within the same stripe.

The name originates from the parity drive rotating forward (right) with each stripe until the start of a new cycle.

This is a rare rotation scheme, used by just a few hardware RAID controllers.

Forw. dyn (aka right-symmetric)

Forward dynamic

Example: RAID-5, 3 drives, block size 128

Local drive
sector *) \

Drive 1

Drive 2

Drive 3

Cycle

Stripe

0-127

B1 **)

128-255

256-383

384-511

512-639

B10

640-767

B11

B12

*)	Sectors, cycles and stripes are 0-based, blocks and drives are 1-based
**)	Blocks B1, B2, B3, ... are data in the 1^st 128 global sectors (0-127), 2^nd 128 global sectors (128-255), 3^rd 128 global sectors (256-383), etc. P is parity for the blocks within the same stripe.

As with the forward rotation, the forward dynamic rotation gets its name from the parity drive rotating forward (right) with each stripe until the start of a new cycle. It is very similar to forward, only stripe 1 arranges the blocks differently. The block to the right of parity P is the block with that stripe's lowest number, while in forward the lowest numbered block is always the first block. The blocks start to the right of parity P, incrementing by 1 with each block, rolling over to the first block and continuing until reaching parity P from the left side. Some people call this right-symmetric.

This rotation scheme is very rare.

Mapping

You can write the mapping of a chosen RAID topology into a text file. Click on Mapping on the bottom. Confirm the file name and the number of sectors in the following dialog:

Press Ok.

The mapping file will look like this:

>

RAID Mapping Report - Sectors 0 to 10000 - 4/11/2020 11:23:07 PM RAID-5, 3 drives, Rotation: Backward, Block size: 128, Start sector: 0 1 stripe has 3 blocks (384 sectors) with data in 2 blocks (256 sectors) and parity in 1 blocks (128 sectors) 1 cycle has 3 stripes, 9 blocks (1152 sectors) with data in 6 blocks (768 sectors) and parity in 3 blocks (384 sectors) LOCAL \ DRIVE-1 DRIVE-2 DRIVE-3 SECTOR # \ ----------- ----------- ----------- \Global sector # 0 |0 128 PARITY 1 |1 129 PARITY 2 |2 130 PARITY : 126 |126 254 PARITY 127 |127 255 PARITY -----------+----------- ----------- ----------- 128 |256 PARITY 384 129 |257 PARITY 385 : 254 |382 PARITY 510 255 |383 PARITY 511 -----------+----------- ----------- ----------- 256 |PARITY 512 640 257 |PARITY 513 641 : 382 |PARITY 638 766 383 |PARITY 639 767 Start of cycle 1 -----------+----------- ----------- ----------- 384 |768 896 PARITY 385 |769 897 PARITY : 510 |894 1022 PARITY 511 |895 1023 PARITY -----------+----------- ----------- ----------- 512 |1024 PARITY 1152 513 |1025 PARITY 1153 : 514 |1026 PARITY 1154 515 |1027 PARITY 1155 638 |1150 PARITY 1278 639 |1151 PARITY 1279 -----------+----------- ----------- ----------- 640 |PARITY 1280 1408 641 |PARITY 1281 1409 : 766 |PARITY 1406 1534 767 |PARITY 1407 1535 Start of cycle 2 -----------+----------- ----------- ----------- 768 |1536 1664 PARITY 769 |1537 1665 PARITY : : : 5374 |PARITY 10622 10750 5375 |PARITY 10623 10751

This is very helpful for research purposes.

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