V2, V3, and 1800 storage disk domain planning

Are there any good suggestions for the planning of V2, V3, and 1800 storage disk domains? Will the storage pool be potentially dangerous if the disk domains are used across disk enclosures? If you do not want to implement the tiered storage function, do you need to put different types of disks into one hard disk box if you do not want to implement the tiered storage function? Will a hard disk domain that does not use hard disks reduce the speed of high-speed hard disks? 

Thanks