December 8, 20214 yr Hi, I have an array with 2 drives, 2To each. 1 as data drive and one as parity. I would like to extend my server by adding 2 new 4To drives 1 as parity and the other as data drive. So 1x2To + 1x 4To as parity and the same as data. But when I'm trying to add the data drive unraid says the parity drive is too small. I tried to swap the 4To drives but, same problem. Any idea of what could be the problem?
December 8, 20214 yr Community Expert Parity isn't a mirror. No parity drive has any of your data. Parity (in any system) is just an extra bit that allows a missing bit to be calculated from all the other bits. Every bit of parity plus every bit of all other disks must be reliably read to reliably rebuild every bit of a failed disk. https://wiki.unraid.net/Manual/Overview#Parity-Protected_Array Dual parity is similar but because of different algorithms the parity drives are independent and each allows for recovery of a disk when combined with all the other disks. So, dual parity will allow you to recover 2 disks at once.
December 8, 20214 yr Community Expert Just now, trurl said: Parity isn't a mirror. Actually, single parity with a single data disk is a mirror simply because of the way parity is calculated. And I think dual parity with a single data disk would turn out to both be mirrors but no good reason to do that.
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