The growing RAID group is a challenge

RAID can hit a dead end when it's not possible to grow the RAID group size, which means that there is no scale-out support. After a point, you cannot grow your RAID-based system, even though you have money. Some systems allow the addition of disk shelves but up to a very limited capacity; however, these new disk shelves put a load on the existing storage controller. So, you can gain some capacity but with a performance trade-off.