Think of a harddrive or chassis of harddrives as simply a place to put data. No RAID or filesystem. Files are grouped together as “objects” which can be any group of complete files. These objects are then chopped up into pieces and spread across storage systems for redundancy. These storage systems can be anywhere.
Because it can use any storage system it can grow large but performance is not great because there is no RAID in place to speed things up. It’s big, redundant and slow generally so it’s good for clouds.