Parity to disk ratio?

[unraidbiff]

Hi all

 

newbie here, couldnt find any threads on this but hoping somebody can direct me if possibe please?   

I see some large unraids arrays in the threads >120TB , i am hoping to have something similar, to begin with 120TB raw in the form of:  
 - 6x 10TB

 - 6x 6TB

 - 6x 4TB

with 6 more bays for future expansion.

 

I had originally been planning for ZFS-Z2 arrays on each however after discovering how damaging it is to consumer SSDs (the OS) i kind of had to throw away that idea.

 

my question is simply that from what i have been able to find here in UNRAID forums, you can only assign 2 parity drives (providing they are at least as large as the largest drive in the pool).  but in my instance the maths doesn't seem to add up, how can 2x 10TB parity provide enough cover the other 16 disks?   

 

perhaps there is some wonderful way of calculating it that i am unaware of but hoping somebody can share some info please?

 

Many Thanks!

G

 

[JonathanM]

1 hour ago, unraidbiff said:

my question is simply that from what i have been able to find here in UNRAID forums, you can only assign 2 parity drives (providing they are at least as large as the largest drive in the pool).  but in my instance the maths doesn't seem to add up, how can 2x 10TB parity provide enough cover the other 16 disks? 

Parity alone doesn't protect anything. Parity plus all the remaining good disks emulate the failed drives. There is NO readable data on the parity disks.

https://wiki.unraid.net/Parity

[unraidbiff]

Brilliant!  thanks very much!