How to define the parity device size

[Leonardo Takahata]

Hello guys!

 

I'm a newbie into unRAID and I'm trying to understand somethings.

 

For now, I need to know how to define the parity device size. See, I will install 2 HDs of 2TB each, one at disk 1 and the other at disk 2.

 

I don't wanna spend a lot, however, I want a efficient parity system.

 

How to choose the right size of the parity HD? 250Gb, 500Gb, 1Tb, 2Tb....???

 

Many thanks

 

Leo

[Tybio]

Parity needs to be the largest disk in the array...if you have 4x2TB drives then just pick one for parity.  If you have an 8TB drive and 2x6TB drives than the 8TB drive has to be your parity drive.

 

Look at it this way, the Parity drive is as large, or larger than all of the other drives in the array.  You can have as many data disks as you want (within the unraid limit at the moment), as long as they are the same size, or smaller than the Parity drive.

Edited May 27, 2018 by Tybio

[Leonardo Takahata]

5 minutes ago, Tybio said:

Parity needs to be the largest disk in the array

 

Thanks for the help Tybio!

So lets imagine I have one 500Gb, one 1Tb and one 2Tb:

0,5 + 1 + 2 = 3,5

So I'll need a 4Tb as a Parity Disk?
 

[Tybio]

No, I wasn't clear enough...my fault.

 

In your example, the 2TB drive would be the parity, giving you 1.5TB of protected space.  It isn't the size of the protected array that matters, only the size of the largest protected disk.

 

For example, if you had the following drives:

 

2: 0.5TB

2: 2TB

1: 10TB

 

You would end up with an array where the 10TB drive is the Parity drive, giving you 5TB of protected storage (.5+.5+2+2=5) but you could get the same thing by using a 2TB drive as parity rather than the 10TB as the largest "protected" disk is only 2TB in size.

 

Does that make more sense?

 

Edit: Let me attach a picture of my current system, you can see that all of my data disks are protected by a single 10TB parity drive

Edited May 27, 2018 by Tybio
Added screen shot

[remotevisitor]

The parity disk must be as large (or larger) than the largest data disk.

 

it doesn’t matter how many data drives you have (other than Unraid license limitations), just what size is the largest data disk.

[Leonardo Takahata]

1 hour ago, remotevisitor said:

The parity disk must be as large (or larger) than the largest data disk.

 

it doesn’t matter how many data drives you have (other than Unraid license limitations), just what size is the largest data disk.

 

Wow, thats great Remotevisitor!

 

I was worried if the data capacity should be bigger than tem SUM of all 

Many thanks!

 

Regards from Brazil!

[Leonardo Takahata]

2 hours ago, Tybio said:

No, I wasn't clear enough...my fault.

 

In your example, the 2TB drive would be the parity, giving you 1.5TB of protected space.  It isn't the size of the protected array that matters, only the size of the largest protected disk.

 

For example, if you had the following drives:

 

2: 0.5TB

2: 2TB

1: 10TB

 

You would end up with an array where the 10TB drive is the Parity drive, giving you 5TB of protected storage (.5+.5+2+2=5) but you could get the same thing by using a 2TB drive as parity rather than the 10TB as the largest "protected" disk is only 2TB in size.

 

Does that make more sense?

 

Edit: Let me attach a picture of my current system, you can see that all of my data disks are protected by a single 10TB parity drive

 

Thanks for the help Tybio!

Very helpful!

 

Leo