I understand that, RAID 3/4 for 4 drives is: Parity Drive = D1 XOR D2 XOR D3. But what is there 5 drives or more? For example 5 or 6. How many parity drives is needed, and how XOR algorithm is working for this case?
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What is the use case for RAID 4 (dedicated parity drive) vs RAID 5, which distributes the parity and resolves any issues with the number of disks in the array? – pmdba Mar 16 '21 at 14:54
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1I see this as more of an educational question. (Which of course makes it off topic for ServerFault.) – Tilman Schmidt Mar 16 '21 at 18:04
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@TilmanSchmidt what is a site of stackexchange for such questions? – Dmitry Sokolov Mar 17 '21 at 19:22
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Super User seems a good choice to me. – Tilman Schmidt Mar 18 '21 at 08:06
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Any number of bits can be XOR'd, and you can always regenerate the data of a failed drive by XORing all the other drives.
This means that this algorithm can only replace a single failed disk, regardless of how many disks are in the array, and it needs to know which disk has failed.
For RAID6, a second checksum disk is used that uses a different algorithm, so the data can still be reconstructed if (any) two disks fail.
Simon Richter
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