Parity planning for 4x10TB drive server

[zolointo]

I'm planning out a server build that will start with four physical 10 TB disks.

 

I've read through the setup docs a few times and am unclear about how parity drives are configured. The documentation says that a parity disk cannot be smaller than the data disk, but I think I'm tripping over the nomenclature of disk/drive/array.

 

I think the goal is single parity, but supported by two disks. Do either of the following accurately describe how I could configure this?

1. Disk 1 + Disk 2 = 20TB Array 1, Disk 3 + Disk 4 = 20TB Array 2, Array 2 assigned as parity disk for Array 1

2. Disk 1 and Disk 2 assigned to a 20TB array, Disk 3 assigned as parity for Disk 1, Disk 4 assigned as parity for Disk 2

 

I'll keep reading/watching, but if you could help me get to an answer faster, that'd be much appreciated!

[trurl]

31 minutes ago, zolointo said:

Do either of the following accurately describe how I could configure this?

No

 

You can have up to 2 parity disks. Each parity disk must be at least as large as the largest single data disk. Single parity allows one missing disk to be calculated from all the other disks, dual parity allows 2 missing disks to be calculated from all the other disks.

 

You can have a large number of data disks of different sizes and only one parity disk, because parity is not a backup and doesn't contain any of your data. 

 

Parity basically is the same concept wherever it is used in computing and communications. It is just an extra bit that allows a missing bit to be calculated from all the other bits. 

[zolointo]

Ah! I think I get it now.

Single parity: 3x10TB data disks with 1x10TB as the parity drive

Dual parity: 2x10TB data disks with 2x10TB as parity disk 1 and parity disk 2

 

Additional drives added to the array must be <= 10TB in order to maintain parity compliance.

 

Very clear now. Thanks for the quick response!

[trurl]

Just now, zolointo said:

I think I get it now.

👍