I have a question that is it impossible to use 3 internal drive, one as a parity and 2 for storage disk with an another external hard drive just for being storage disk without parity for this drive? How much capacity I would get from this setup?

 

Thank you

Hello and welcome.

 

You can do this.  Your "array" would be the parity drive and the two data drives.  Your usable capacity would be the sum of the two data drives.  You'd mount the external drive via the Unassigned Devices plugin.  Since it would not officially be part of the array, it would not be protected by parity and its capacity would not count towards the total managed by the array.  You can get Unassigned Devices via Community Applications .

Do I need same capacity as my data drive for a parity drive?

34 minutes ago, thetkpark said:

Do I need same capacity as my data drive for a parity drive?

You'd need a parity drive that is the same size or bigger than your datadrives (individually not combined). You cannot use a parity disk that is smaller than your data disks. 

If you've got lets say 2x 4TB drives, the parity-disk will need to be 4TB or bigger (lets say 6TB if you plan on using bigger datadisks in the future as the price point will be more economically viable). You can also upgrade your parity drive any time.

If you've got different sized datadisks, parity will need to be the same (or bigger) than your largest drive in the array. 

 

5 hours ago, thetkpark said:

Do I need same capacity as my data drive for a parity drive?

 

The answer given is correct. But wanted to provide more detail. This info will help keep you from shooting yourself in the foot when something goes wrong.

 

This concept of how parity works is fundamental. We have people that think that with parity alone, you can rebuild every disk in the array! What a trick that would be. No - parity is pretty simple and allows reconstruction at a very elemental level if every other disk is functioning and perfect. And only an entire disk can be rebuilt, not a file or directory. And the reconstructed disks is an absolute mirror image of the source.

 

Think of parity as working across all of the drives. If the capacity is the height - parity has to be as tall or taller than the other drives.

 

That's because parity works across all of the drives. The corresponding bits (1s and 0s) across all the drives + parity has to be even. So if the sum of the data disk bits is ODD, parity is 1 (making the sum even), and if the sum of the data disk bits is EVEN, parity is 0 (keeping the sum even).

 

If a disk fails, unRAID can now rebuild it, by adding up the corresponding bits on the remaining data disks + parity, and reconstructing the missing disk bit by bit as it goes. For each bit, If the sum of the other disks is odd, the missing bit is a 1, and if the sum of the others is even, the missing bit is 0. If parity were smaller than the biggest disk, parity would run out of gas and be unable to reconstruct the failed disk from its "height" on.  So unRAID does not allow a smaller parity.

 

Parity 2 works similarly - using more complex mathematics. Parity or Parity 2 can rebuild a single failed data disk. But working together, Pairty+Parity2 can rebuild 2 missing data disks. And before you ask - no, parity and parity2 do not need to be the same size - so long as they are each bigger than the biggest data disk.

 

Welcome aboard and enjoy your array!!

Thank you so much. These reply help me a lot