I plan on jumping to unraid in the next couple weeks but I want to make sure I buy the proper equipment for my setup.  I currently have about 3.5 tb of data on a 4 tb drive (Drive A).  I also recently got a 3tb drive (Drive B) that is empty and ready to put in the unraid.  So from my understanding is this the right way to handle my situation (ignore the data transfer and handling, that may be a separate topic):

 

Purchase a 4 tb (Drive C) or less drive

Preclear all 3 drives

Assign Drive A as parity

Assign Drive B & C as storage

 

Essentially, Parity >= largest Storage drive

Yes, purchasing another 4TB drive is a good idea. I would not get anything less, or more.

When you start unRAID, it can be one of your data drives, along with the blank 3TB Drive B.

You can copy your 3.5TB of data off Drive A onto the array of Drive B and Drive C.

Then add that 4TB Drive A as the parity drive.

 

If the new drive is more than 4TB, the existing 4TB can not become parity.

If the new drive is less than 4TB, the 4TB can be parity, but it slightly oversized (aka stranded capacity).

Depends on the pricing of a 3TB I guess, but I'd get a 4TB.

I plan on jumping to unraid in the next couple weeks but I want to make sure I buy the proper equipment for my setup.  I currently have about 3.5 tb of data on a 4 tb drive (Drive A).  I also recently got a 3tb drive (Drive B) that is empty and ready to put in the unraid.  So from my understanding is this the right way to handle my situation (ignore the data transfer and handling, that may be a separate topic):

 

Purchase a 4 tb (Drive C) or less drive

Preclear all 3 drives

Assign Drive A as parity

Assign Drive B & C as storage

 

Essentially, Parity >= largest Storage drive

 

Preclearing is recommended for new disks. If Drives A and B have been in service for a while and are already  battle tested, preclearing is not necessary.

 

If you preclear your Drive A, you will loose all of the data on it. That would be bad.

 

I like c3's solution. Buy a new drive, Drive C, that is 4T.

 

Preclear Drive C (and Drive B too if it is new and untested).

 

Create array with no parity and Drive B and C installed as Disk1 and Disk2.

 

Copy data from Drive A to Disk1 and/or Disk2 as desired.

 

Do whatever data comparisons etc to ensure data copied properly. (md5?)

 

Stop array and assign Drive A as parity.

 

Start array.

 

Parity will build.

 

Run a parity check to ensure array is functioning properly.