[SOLVED] Parity Swap Procedure

[shimee]

Hi Guys,

Ive just read the process online for this (https://wiki.lime-technology.com/The_parity_swap_procedure), I just have a question before I take the plunge. I currently have a failed data disk (3TB) and am taking the opportunity to upgrade the parity to 6TB and replace the faulty data disk with a 6TB also. As the existing data disk is faulty and says 'Contents Emulated', am I at risk of losing all of the disks data if I go about this process in the wrong order? ie if I swap out the parity, it will rebuild from the data drives, but drive 6 is faulty. So do I need to do the disk replace first, but unable to use the 6TB?

 

Apologies if this is a stupid question I just dont want to risk the data loss.

 

Thanks

 

 

Edited August 17, 2017 by shimee
solved

[trurl]

I've not done it, but I think after it copies parity to the new parity disk, it rebuilds the failed data to the old parity disk. I don't think it will let you substitute another data disk. Maybe @johnnie.black knows.

[shimee]

Thanks trurl,

I guess Im not doing exactly what that process speaks of, in that im not re-using the old parity as a data disk. I think if I was there would be no issue as the new parity drive is larger than the old one. 

 

I assume, probably incorrectly, that when a disk says Contents Emulated, it means the data on the parity drive is being referenced as the data for that disk? If so, I am assuming when the parity is rebuild from disk data, I'd lose my faulty disk data.

 

 

[JorgeB]

The procedure has to be done in that order, first copy the parity disk, then do the rebuild, IIRC you can replace the disk to rebuild with a a different one before starting when unRAID pauses after the parity copy.

[trurl]

7 hours ago, shimee said:

I assume, probably incorrectly, that when a disk says Contents Emulated, it means the data on the parity drive is being referenced as the data for that disk? If so, I am assuming when the parity is rebuild from disk data, I'd lose my faulty disk data.

Not entirely sure I understand what you meant, but it does seem mostly incorrect. unRAID emulates a disk by reading parity plus all the other disks. Parity by itself doesn't have the capacity to reconstruct any and all disks in your array, obviously.

 

And the parity swap procedure doesn't rebuild parity at all. It copies parity and then rebuilds the data disk.

 

Parity isn't particularly complicated, and understanding it can help make a lot of things about unRAID make much more sense.

 

See here for a better understanding of how parity works:

 

https://wiki.lime-technology.com/UnRAID_Manual_6#Parity-Protected_Array

[shimee]

Aah ok, aside from the misunderstanding of the way parity works, I was mostly worried that the parity swap would do a parity rebuild.

 

Thank you for the help, now the long journey begins....preclear has started

 

 

Edited August 17, 2017 by shimee

[JorgeB]

6 hours ago, johnnie.black said:

IIRC you can replace the disk to rebuild with a a different one before starting when unRAID pauses after the parity copy.

 

Wasn't sure about this, but I was wrong, you'll need to rebuild to the old parity, only after that can o upgrade that disk, unRAID pauses before the rebuild but it doesn't allow to rebuild to a different disk.

Edited August 17, 2017 by johnnie.black