My current unRAID configuration has 1 parity (10TB) and 4 data (6TB) drives. I can see how adding a second parity drive protects the array from a parity drive failure, but are there other ways a second parity drive protects the array?

 

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Basically the number of parities is the number of simultaneous missing disks you can recover from. If you are diligent (do you have Notifications setup?) this is less likely the fewer disks you have.

So is the data array plus the first parity drive included in the second parity drive's hash? And that would provide the protection in case a parity drive and a data drive fail simultaneously (or 2 data drives for that matter)?

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You might want to read this threaed:

 

 

1 minute ago, dchamb said:

So is the data array plus the first parity drive included in the second parity drive's hash? And that would provide the protection in case a parity drive and a data drive fail simultaneously (or 2 data drives for that matter)?

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Parity isn't exactly a hash. It is actually much simpler. Understanding parity is pretty easy and if you understand it you will already know the answer to a lot of questions. Many things about how unRAID operates will make more sense, and you are less likely to make mistakes when you need to operate unRAID.

 

https://lime-technology.com/wiki/index.php/UnRAID_6/Overview#Parity-Protected_Array

And parity2 is a little more complicated, but similar to the way parity is described in the wiki, still working with bits across disks.