July 30, 20196 yr Hey everyone. This is probably Unraid 101, so I'm sorry if it's a "go read the wiki" kind of question. But I want to make sure I do this right the first time. Until now, I've been using Unraid with only one 2TB HDD in my array. Today, I added a 1TB NVME disk for cache + VM images (already set up) and a 4TB HDD that I want to use for redundancy. Being that the new drive is larger, I understand it has to be the parity drive. What is the process I should follow here? Currently, both HDDs are assigned to the array, with the new one being empty. Thanks!
July 30, 20196 yr Community Expert You'll need to do a new config (tools -> new config), then keep other assignments and re-assign the 4TB disk as parity.
July 31, 20196 yr Author On 7/30/2019 at 12:53 AM, johnnie.black said: You'll need to do a new config (tools -> new config), then keep other assignments and re-assign the 4TB disk as parity. Should I copy everything over from the other drive first? If I leave the new disk empty and set it as parity, won't it erase the data on the current disk?
July 31, 20196 yr Community Expert 1 hour ago, cyberspectre said: Should I copy everything over from the other drive first? If I leave the new disk empty and set it as parity, won't it erase the data on the current disk? You said the disk you intend to assign to parity is empty. What is there to copy? When you New Config, the disk you assign as parity will be completely overwritten with parity. No other disks will be changed. Shouldn't happen, but just in case, if it offers to Format anything, DON'T.
July 31, 20196 yr Author 4 minutes ago, trurl said: You said the disk you intend to assign to parity is empty. What is there to copy? When you New Config, the disk you assign as parity will be completely overwritten with parity. No other disks will be changed. Shouldn't happen, but just in case, if it offers to Format anything, DON'T. Oh, I see. I think I was looking at it the wrong way around. I was under the impression the parity was the "master" disk and all data disks mirror what's on that.
July 31, 20196 yr Community Expert Parity actually contains none of your data. Parity just contains parity bits that allow the data for a missing disk to be calculated using the data from all the other disks. The concept of parity is pretty common in computers and communications. It is always just a bit that allows a missing bit to be calculated from all the other bits. So, all the other bits are required for the calculation to work. If you have dual parity, then you can have 2 missing disks and still calculate them from all the remaining disks. Here is a wiki article on how Unraid parity works: https://wiki.unraid.net/UnRAID_6/Overview#Parity-Protected_Array
August 2, 20196 yr Author On 7/31/2019 at 4:52 PM, trurl said: Parity actually contains none of your data. Parity just contains parity bits that allow the data for a missing disk to be calculated using the data from all the other disks. The concept of parity is pretty common in computers and communications. It is always just a bit that allows a missing bit to be calculated from all the other bits. So, all the other bits are required for the calculation to work. If you have dual parity, then you can have 2 missing disks and still calculate them from all the remaining disks. Here is a wiki article on how Unraid parity works: https://wiki.unraid.net/UnRAID_6/Overview#Parity-Protected_Array Thanks trurl. I've got it figured out now. Larger disk set as parity, which, in a 2-disk array, is actually a mirrored setup. Exactly what I needed.
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