Dear Unraiders

I am in the following situation:

I have an array of 16 Disks with 1 Parity. I have a full Backup of the data but restoring would take a lot of time and costs involved.

I would like to minimize downtime.

The Array consists of 11 20TB drives and 5 16TB drives. The parity is 20TB.

I bought 2 28 TB drives and they are precleared as a stress test.

I want to add both drives to the array. Since the new drives are bigger than the current ones - I need to change the parity drive. I would like to to this without letting the array unprotected.

If I understand the documentation correctly, it suggest to simply replace the parity drive and let it rebuild. This means the array is unprotected - which I dont want.

Is this a possible (and safe) way to add the 2 28TB disks:

1. Add 1 28TB disk as 2nd parity drive.

2. Remove parity 1 and put the 2nd 28TB disk in - let it rebuild parity 1 (if a drive fails, I can simply rebuild since there is parity 2 right?)

3. Preclear the old 20TB parity drive.

4. Add it to the array

5. Remove Parity 2 and restart the array

6. Preclear Parity 2

7. Add the 28 precleared disk to the array as new data drive

In my head, this way will take some time - but also should be the safest way right?

Also in theory, I will have only 3 downtimes to add / remove the specific drives.

Can I rebuild if Parity 1 is being rebuild and a data drive fails (in other words: Rebuild a data drive if I can only have parity 2?)

Thank you very much for your help - I am also open to simpler solutions - as long as the array is protected.

Thanks!

Edited November 1, 2025Nov 1 by gandalf15

Your approach would work.

If you do not mind ending up with a parity2 and no parity1 then steps 2-6 could become.

• add old 20TB parity1 disk to array AND new 28TB disk.

• Start array and let Unraid "Clear" them (which is faster than preclear).

Note that preclear is really intended to stress test a drive so you can instead let Unraid "Clear" drives as needed if you do not want the stress test.

Thank you very much!

Does it make a difference if I end with only parity2 instead of parity1? I read that parity2 uses a different calculation than parity1.I read somewhere that if you only have parity 2 the array will always show as unstable. But I have never had 2 parity drives.

Indeed the preclear after removing parity is not necessary - I already stress tested those recertified drives. I wanted to do it to keep downtime minimal. I think I also read to clear a drive the array is not usable - and since 28TB took 30 hours to write all 0 I thought I might just use preclear to directly restart the array.

4 hours ago, gandalf15 said:

Does it make a difference if I end with only parity2 instead of parity1? I read that parity2 uses a different calculation than parity1.I read somewhere that if you only have parity 2 the array will always show as unstable. But I have never had 2 parity drives.

You are correct that parity2 uses a different calculation to parity1, but there is no problem having parity2 and no parity1. Never heard before about parity2 causing any sort of stability issues.

4 hours ago, gandalf15 said:

think I also read to clear a drive the array is not usable

That was true in earlier Unraid releases but it has not been the case for some time now and the clear runs as a background task having little impact on system performance.

What is true is that the drive is not usable for storing data until the Clear finishes and you format the drive.

Thank you - then all is clear.

Tomorrow I will toss in Parity 2 (new precleared (as a strestest) drive) into parity 2 - once its fully rebuild as parity 2, i will remove the old parity 1 and set it as a data drive and at the same time add the new data drive.

Thank you very much!