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jj lolo

Unraid drive reliability calculator?

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I've just build a NAS to use for either unraid or xpenology and just ordered 4x14TB seagate enterprise drives.


I'm trying to compare unraid vs raid 5 and 6 reliability rates (including a full recovery- as we all know other drives can fail during the recovery period). While I understand that data loss is more limited, I'm wondering how to calculate the chance of ANY data loss.


Using https://wintelguy.com/raidmttdl.pl and the variables below,


Using raid 5- I get a probability of data loss over 10 years of 0.0014504202932147

And with raid 6 I get a probability of data loss over 10 years of 0.0000002555505010


1. I was wondering what they would be for unraid with one and two parity drives since I couldn't find an online reliability calculator for unraid? Or is it simply the same as above but if loss occurred instead of loosing 100% of your data you loose some?

2. Is there a way to numerize the probablility?

3. How fast are the rebuild times compared to traditional raid 5/6?

4. I didn't find a space calculator other than for just one parity drive. Is there one? Are there speed advantages (e.g. Raid 6 has 2X read speeds).

5. Which license would I need?


Thanks in advance for your help!


Here were the variables I used:

Total Usable Storage Capacity (GB)  42000
Number of RAID Groups 1
Number of drives per RAID Group 4
Total Number of Drives: 4
Drive Capacity (GB) 14000
Throughput (MB/s) 600
Drive MTBF (hour) 876000
Drive Annual Failure Rate (%) 1

Edited by jj lolo

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Total capacity is simply the total of all data drives. Doesn't matter if you have 1 or 2 or zero parity drives. 


Also each data drive is an independent filesystem, no striping. So each data drive can be read by itself in any Linux. 


Read speed is the speed of the individual disk. Write speed somewhat slower due to parity update. 


Unraid is not RAID. It has other advantages, such as the ability to read any disk without the others, the ability to easily add more disks without rebuilding, and the ability to use disks of different sizes together in the array. 

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Thanks for the explanation. I understand that each drive is independent and could be read directly.


I guess what I don't understand is that if in my case I have 1 parity drive, and 3 data drives (4X14TB total disks) drives how the parity drive can duplicate the data of the 3X data drives and store 3X14TB of data on just one 14tb drive and say if one of the data drives dies, then how it can recreate the contents of that drive from just 1 parity drive, and in that scenario, how long it takes and the calculated failure rate could be on rebuilding such a large drive? What am I missing?


Similarly, if I'm paranoid, and have two parity drives, how is performance impacted?


What would you recommend as the ratio of parity vs non parity drives?


What is the disadvantage of unraid?

Edited by jj lolo

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A failed drive is not simply calculated from parity!     It is calculated using the combination of all the ‘good’ data drives plus the parity drive.   This is why you need reliable drives in the array.    The wiki has a good description of how parity works so reading that might clarify things.

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You might want to review this thread:





But remember that the security of your data is also dependent on you keeping running (at least) monthly parity checks, maintaining a watch on the health of the system via the notification setup and taking action as soon as some problem comes up.  Plus, if you go with dual parity, the probability of data loss due to another causes (fire, theft, lightning, flooding, operator error, etc.) is more likely.   No single server should be the only storage point for irreplaceable data.  You need two more storage solutions for that-- one of them off-site. 


EDIT: for the WIKI that describes how single parity worrks see here:




The second parity drive (dual parity) basically works the same way with a lot more math.  

Edited by Frank1940

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