Dual Parity question....

[jbuszkie]

This is probably another dumb question...  But I want to add a second parity disk (10TB).  I'll assign it to the parity 2 slot.  Now if for some reason I need the disk space and I want to go back to one parity disk...  Can I get rid of the Parity 1 (8TB) disk and just have single parity on the parity 2 slot?  Or do I have to re-assign the 10TB to Parity 1 and have to rebuild parity completely?

 

Jim

 

Edit:  I will eventually make both parity 10TB..  But for now I'll stick with a 8TB array limit..

Edited March 13, 2020 by jbuszkie

[itimpi]

Yes, you can run with either (or both) parity drives missing.

 

if later you want to add back a parity drive simply assign it and Unraid will start to build parity on that drive.

[JonathanM]

2 hours ago, jbuszkie said:

Can I get rid of the Parity 1 (8TB) disk and just have single parity on the parity 2 slot?

To expand on that a little, the two parity slots are completely different. You can't take a drive that was valid in parity1 and assign it to parity2 and have it still be valid, it must be rebuilt. Data drive slot reassignments don't invalidate parity1 as long as the same drives are used, but parity2 must be rebuilt if you swap data slot assignments.

 

Each parity slot can rebuild 1 data slot, independent of the other parity slot. Having only 1 parity drive in parity2 works just fine, it's a bit more complex mathematically, so the CPU works ever so slightly harder.

 

In retrospect, I kind of wish that when the change was made to add the second parity slot that things were renamed to make the difference clearer. Maybe something like "Basic Parity" and "Complex Parity". Maybe not. It's tough to convey all the nuances with simple labels.

[jbuszkie]

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Having only 1 parity drive in parity2 works just fine,

That's what I was looking for...

 

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it's a bit more complex mathematically, so the CPU works ever so slightly harder.

Very interesting and good to know.

I knew that the 2nd parity uses drive position..  But I didn't know that it was the Parity 2 slot..  not just a 2nd parity drive!