JBOD (which stands for "just a bunch of disks") generally refers to a collection of hard disks that have not been configured to act as a redundant array of independent disks (RAID) array.
RAID arrays write data across multiple disks as a way of storing data redundantly (to achieve fault tolerance) or to stripe data across multiple disks to get better performance than anyone disk could provide on its own. Typically, a RAID array will appear to the operating system as a single disk.
JBOD is an alternative to using a RAID configuration. Rather than configuring a storage array to use a RAID level, the disks within the array are either spanned or treated as independent disks. Spanning configurations use a technique called concatenation to combine the capacity of all of the disks into a single, large logical disk. Although some RAID levels also concatenate disks, numbered RAID levels generally use striping or parity while JBOD does not.
Figure 1: A schematic example of a JBOD storage system
JBOD means the individual disks are presented (to a server) with no amalgamation, pooling or structure applied. The term is in widespread use, especially in the context of computers that have software volume management, such as LVM (AIX, HP-UX, Linux), DiskSuite (Solaris), ZFS (Solaris), Veritas Volume Manager (Unixes), Windows and so on.
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