There's 3 types of enclosures that hold a whole bunch of hard drives. There's:
Let's talk about each one a little more.
JBODs are the most basic type of enclosures. JBOD stands for Just a Bunch of Disks, yes that's actually what it stands for. The reason behind that name is because it doesn't do anything. All it allows you to do is plug it into a server or a RAID enclosure and add more hard drives to that existing server or RAID enclosure.
If you plug a JBOD into a computer you would see each of those drives in your disk management utilities.
Because JBODs are so simple they are the least expensive option for adding more storage to your existing infrastructure.
A RAID enclosure goes one step beyond a JBOD. With a RAID enclosure you put your hard drives in it, but it has a RAID controller built in (usually a hardware controller). So when you connect to a RAID controller you will just see that single RAID 5 or RAID 6. There's always some software involved as well. Common types of these enclosures include Thunderbolt RAID systems like a G-RAID or a Promise 8-Bay Thunderbolt RAID.
Now the most complex and most intelligent of these options is a server. This is when you have an enclosure that has a motherboard, a processor, RAM and an OS. This is what most of us are familiar with. When you buy a new network storage system this is what you are getting. Typically you would use a JBOD to expand one of these systems.
So when you're buying these systems be aware of what you are getting and what level of intelligence you are adding to your infrastructure, each one of them has their upsides and downsides.