3 drives volume: which is the best option to replace all drives?

Hello community
i have a Synology NAS DS1621+ with 6 bays
Right now I have a volume of 3 drives 6Tb each for all my files, and another volume of 1 drive 4Tb for surveillance and timecapsule
I have just got 3 additional drives 8 Tb each and I would like to replace all the 6Th drives of the main volume
Which of the following options do you recommend:

  1. deactivate one 6 Tb drive, replace it with a 8 Tb drive, let the system rebuild integrity of the volume, then deactivate another 6 Tb drive and so on until the end

  2. remove the 4Tb drive for a while (I assume the volume and the folders setup will remain in my DS but it will just warn me that the drive is missing) then install all three 8 Tb drives, create a new volume on its own, then one shared folder at a time, move it from the current three 6Tb drives’ volume to the new three 8 Tb drives’volume

  3. other options I am not thinking of

Many thanks!

If you work with snapshots option 1 is your friend.