Just a Bunch Of Disks
JBOD is a system that allows you to combine several hard disk drives as if they were a single disk. For example, if you have a 20 GB hard disk drive and a 40 GB one installed on the same PC and configure them to use JBOD, the operating system will show them as a single 60 GB drive.
Even though several people consider JBOD a RAID system, this is not true, since it doesn't have none of the two basic RAID concepts: reliability increase and performance increase. JBOD system does not increase the system reliability or its performance.
We can consider JBOD the opposite of partitioning: while partitioning divides one physical hard disk drive into several logical disks, JBOD combine several physical disks into a single logical unit.