Choosing correct RAID then also expanding individual HDD size in either RAID 5 or RAID 10

To preface, I am very new to RAID as I currently have my EX4100 in Spanning and now want redundancy.

My current setup is
Drive Bay 1- 6 TB
Drive Bay 2- 6 TB
Drive Bay 3 - 12 TB (not yet configured)
Drive Bay 4 - empty

I am currently moving all my data to external HDD so I can create the RAID then copy all data back to the NAS, this is a process I don’t want to do again.

I understand RAID 10 provides the best redundancy So thats prob the path that I’ll go.

But my question is relatively the same for both setups.

At this stage i am looking at puttingvanother WD red 12tb in bay 4. But as I am shooting a fair bit of 4k video and the megapixel count of cameras get larger, as does their RAW file size, I know I’ll fill up these hard drives pretty quick (especially if I go raid 10). Which will draw my attention back to drive bays 1 and 2

If in the future I upgrade them to say a 12tb each but replace the drives 1 at a time, will the data be automatically moved to the new one. E.g. I upgrade drive 1 to a 12tb but leave drive 2 in, will the data from drive 2 be automatically written onto drive 1 without me having to do it manually…and then repeat when I replace drive 2. And once both replaced I’ll have an extra 6tb to play with (that being the delta between the old drive size and the new drive).

Same question around RAID 5, if I replace and upgrade the size of drive bay 1 and 2 in the future will the data that was in the old smaller drives be written onto the newer larger ones and give me additional space to play with?

Knowing these answers will go a long way to determining the way I go ahead

Thanks in advance for all your help and I hope my question and dilemma makes sense

Yes, if you replace a drive in a RAID array one at a time and let the array rebuild after each replacement, the data will automatically be moved to the new drive. This is known as “rebuilding” the RAID array. The process of rebuilding will take some time, during which the array is operating in a degraded state, but once it is complete, the array will be restored to full redundancy.

However, when upgrading the drives in a RAID array, it is important to replace them with drives of equal or greater capacity than the existing drives. If you replace a smaller drive with a larger drive, the extra space on the larger drive will not be used in the RAID array. Instead, the extra space will be unused and wasted until all the drives in the array are replaced with drives of equal or greater capacity. This is true for both RAID 5 and RAID 10.

So, in your case, if you replace drive 1 and 2 with 12TB drives one at a time, the new drives will rebuild the array, but you will not gain any additional space until you replace all four drives with 12TB drives. If you replace all four drives with 12TB drives, you will have a total usable space of 24TB in a RAID 10 array or 36TB in a RAID 5 array (minus the overhead of the RAID configuration).

I hope this helps!