it might be optional but I will say that is highly recommended, the way I do it, I always create a new raid I think I understand your question, I done so many test, betas etc and I do remember some time in the past having some problems, let me explain, yes it should work meaning just erasing the raid not braking the raid but I think is better to break the raid and create it new using High Sierra installer or brake the raid that you already have from HS OS and create a new raid using High Sierra raid assistant, I think is better like this so you can avoid any problem, creating a new raid is better so you know you will not have any problem when installing the system. You can create the raid0 volume using the Mac OS that you already have installed then use a command to dump Mac OS 10.13.4 installer onto the raid0 drive, now all you have to do is run the installer that is inside the raid0 volume and when you Mac restart it will do everything and you will have to do is wait until it finishes There is also another way, but it requires that you have the copy of Mac OS 10.13.4 that you downloaded from the app store in applications

To clone your already installed system to the raid0 volume You can also create the raid0 on you already bootable Mac OS then use carbon copy cloner Now simply install Mac OS on the raid0 volume Remember it has to be in Mac OS journaled Raid assistant will combined both drives and it will create a raid0 volume Now go to raid assistant and select raid0, select your stripe size and select the drive that you will like to use to create the raid0 volume or array I didn't upgrade, I always like to clean installĬreate the usb flash installer, backup all your data, load the installer, once you thereĮrase the ssd drives and make sure they are on Mac OS journaled and not APFS Yes right now I have Mac OS 10.13.4 in raid0 bootable You can install on a single drive then clone that drive to a raid array but you can also create the raid array when you are going to install Mac OS from disk utility in Mac OS installer so technically if you want raid0 on HS you have to give up APFS Yes you can do it like that too, but in order for the raid0 to be bootable it has to be formatted on mac os journaled.

How to clean install macos high sierra