New Config Tool for adding smaller drives?

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Hey folks,


I'm new to Unraid, but I totally love it. It's a big improvement, coming from OMV and generic raspi NAS's. I'm adjusting my configuration and have some concerns before I press the big red button.


Bottom Line Up Front: I'm thinking I should use the 'New Config' tool to add new disks to my array that are smaller in capacity than my current disk in order to establish smaller drive capacities and maintain parity protection. I'm unsure though, whether this is the correct way forward.


Details: I had an array with (1) 18 TB data drive and (1) 18 TB parity drive. Things worked great but I was nearing 15 TB of data so I decided to add some old external drives to the array as data disks. These were (1) 10 TB and (1) 8 TB drive.


As I understand it, Unraid must use the smallest disk's capacity on all drives to maintain parity. So, all 3 data disks should only have 8 TB of usable space, for a grand total of 24 TB. I installed the drives, added them to the array, and Unraid cleaned and formatted them. They're now showing in my pool as usable drives, but all of my data disks still have their full capacities with a total of 36 TB showing up.


Again, I think I need to run the 'New Config' tool in order to properly set the disks' max capacities to 8 TB and re-establish parity. However, I'm not sure this would work the way I think it would and I have some questions that I haven't been able to find in the manual or in other posts....


- Would Unraid avoid data loss by 'balancing' the 18 TB disk? I.e. send data to the other drives before reducing its max capacity to 8 TB?

- Is there another way to do this that I'm simply not considering?


I appreciate ya'lls input!

Edited by darkphox
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With single disk parity the parity calculation is just the sum of all the corresponding bits on each disk. For example, if the sum of the first bit on each disk is odd then it’s possible to determine wether that bit should be 0 or 1 on a single missing disk. This means that the parity drive size must be the same or larger than any other disk so that it has the total of every bit but smaller drives don’t limit total capacity.

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1 hour ago, darkphox said:

I decided to add some old external drives to the array as data disks.

Please keep in mind that parity protection relies on ALL remaining data disks to reconstruct a failed drive. So, if your shiny new 18TB drive fails, you will be relying on those old drives to be read perfectly across their entire capacity to reconstruct a replacement drive. If one of those old drives happens to have a read error on any sector, not just areas currently used for data, the rebuild will have errors.


You must not allow any drives that aren't perfect to participate in the parity array.


Make sure you run a non-correcting parity check after all the drives are added, zero errors is the only acceptable result. It wouldn't hurt to do a long smart check on all the drives as well.

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Thanks Jon, I'm tracking. I use the term 'old' relatively. They're about a year old and are the drives from my raspi NAS setup. I also have another 18TB drive in the pipe for a 2nd parity disk, and I still have everything redundant on my old OMV setup. Just got confused (somehow) on the impact (or lack thereof) of mixed disk sizes. Again, loving far the best experience I've had with this type of thing.

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