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Based on this question about RAID-5 for 5 disks: Two disks failed simultaneously?

Sorry if I butcher some of the terminology

Why is a double disk failure an issue for a 5 disk Raid 5 configuration? Even with 2 disks offline, I still can access the sections (terminology?) A, B, C, D and E. Assuming there is no disagreements (terminology?) between (D1 and D2) OR (E1 and E2), I don't see why a double disk failure couldn't continue to work and rebuild 2 new drives.

If you lose more than a single disk in a RAID 5, your array has been irreperably damaged in some way. In most cases, the data is entirely destroyed in your case if you're not an expert at recovery, or if you are unwilling to ship it off to a recovery outfit. - SmallLoanOf1M https://serverfault.com/a/834147/348076

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Paul Totzke
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You are not able to read the A4 data in the stripe in this instance. And you are also unable to read the Parity info to rebuild the data from the Parity information for stripe A.

Therefore, you have data loss and are not able to recover/read the data.

Rex
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Exactly, where the confusion here is how the data is saved.

Using the graphic above, if you were to save a block of data of "ABCDEFG", then you would have "ABCD_FG". Because the volume that the E has failed, the controller would need to "rebuild" the missing block of data from the parity drive. However, since the parity drive is also failed, there is no way to recover the 'E' piece of data.

This is where RAID 6 comes into play to better save your data.

Jean-Claude DuBois
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