So my NAS is currently approaching being full. It has 8 total available SATA ports (4 on mobo, 4 on pcie card that occupies the only pcie slot on the mobo) and they are all currently populated with: 3x 12TB drives (1 is parity), 3x 4TB drives, and 2x 512GB SSDs (redundant cache pool)

The end goal is to replace the 3x 4TB drives with 3x 24TB drives, but I know that the parity drive must be at least matched in size with the largest hard drive in the array, so one of the 24TB drives will need to become the new parity drive.

So my questions boil down to: What is the best order of operations for getting from A to B, and what does that look like every step of the way?

There are no drives in the array that don't have data on them, so would it be best to disconnect the current parity drive and replace it with a 24TB drive, and then <tell it to use the new drive as parity (not sure how)>?

And then from there how do I migrate the other drives without losing data or having to manually transfer them by buying a SATA to USB dock or similar?

1.) 12TB parity -> 24TB parity, build new parity (don't know how to do this)
2.) 4TB data -> 24TB data, rebuild from parity (don't know how to do this)
3.) 4TB data -> 24TB data, rebuild from parity (^)
4.) 4TB data -> 12TB old parity, rebuild from parity (wipe it first? can unraid handle that for me? how?)

Or does it make more sense to first temporarily replace one of the SSDs from the cache with the new 24TB parity drive and let it switch over that way?
Does it matter what SATA port each drive is plugged into? I know Windows is really dumb and picky about that.

Just seems like there are a lot of paths forward, and I'm not sure what makes the most sense, and I'm very paranoid about losing any of my data in the process.

Thanks!

Edited July 23, 2025Jul 23 by albrittbrat91

Read this section of the manual and come back if you still have questions.

https://docs.unraid.net/unraid-os/manual/storage-management/#replacing-a-disk-to-increase-capacity

If you just remove the drive you are replacing and set it aside until you are sure all is well, you will be protected from data loss. That drive is your backup! (Unraid array data drives are formatted with a standard Linux File system and the contents of that drive-- your data files --can be read by any Linux system.)

PS--- I would buy two 24TB drives to begin with and get the next one (1) when you are again running out of storage space or (2) if you find a good sale price! And I keep a 'cold' spare drive...

BTW, you can repurpose that old 12TB parity as a data drive using the same procedure.