Alternate MIRROR RAID geometry could double the speed of reading and writing

The placement of data in a classic mirror o raid 1 is as follows

D1: [0] [1] [2] [3] [4] [5] [6] [7]
D2: [0] [1] [2] [3] [4] [5] [6] [7]

This gives the following performance in terms of speed, capacity, and fault tolerance:

Speed: the original disk (it is assumed that the 2 disks are identical)
Capacity: from one of the discs
Fault probability: p ^ 2, being p probability of a single disk failure during a given time

But lets consider this placement... :

D1: [0] [2] [4] [6] [1] [3] [5] [7]
D2: [1] [3] [5] [7] [0] [2] [4] [6]

In the first middle of the mirror, in fact, we have a strippe, in the second half, a symmetric strippe. The controller in fact works as a common stripe for reading but needs to duplicate writting operations as in a common mirror. In case of failure of one of the 2 disks, the performance would be bad due to fragmentation, that's a drawback.

This' mirroring ' could use 3 or more disks, which can increase the reading speed while leaving writting speed constant. We always get a logical space that is half of the total physical.

D1: [0] [3] [6] [9] [1] [4] [7] [A]
D2: [1] [4] [7] [A] [2] [5] [8] [B]
D3: [2] [5] [8] [B] [0] [3] [6] [9]

The weakness of this geometry is the performance drop in case of a disk, and the constant writting speed. If someone could improve one of this points...

Even with these drawbacks I think is an interesting intermediate point between the stripper and classic mirrors. A mirror with the reading speed of a stripe using only two disks.
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Creado por

maguilar

maguilar

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  • maguilar
    20 de agosto 01:14

    Sorry, I made a few mistakes... first, the title is wrong, only reading speed is increased, second, I forget to said that the controller does not need to perform calculations but does need a big cache to be able to write a lot of data before being forced to move to the other half of the disk, otherwise, writing would be very slow. A big amount of data would need to move the heads too much. third, excuse my English.

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