Have dual parity drives, however one of them failed. All the drives are 3TB in size including the parity drives but when one failed I replaced it with a 5TB drive and that one failed too. My question is now I have dual parity mismatched one is 3tb and the other is 5tb can I downgrade that 5TB drive that failed back to a 3TB drive?. I know in raid system you can use different sizes of drives but you only going to get the smaller capacity of the drives and since the other parity drive is 3TB I may be assuming that the 5TB is only using 3TB capacity. Thanks in advanced 

To do that, you have to do a New Config

 

But, the better question is why do you think that 2 drives failed...  Actual drive failures are rare.  Far more often are connection problems.

Perfect why didn't I thought of that ? so new config on the parity drives and keep configuration on the cache and data drives. This is my third UnRaid server I own and is build of old parts. Thanks for the advice