RAID gets all the attention nowadays, but there’s still a place for RAID’s less talented cousin, JBOD.  Both are comprised of multiple physical drives, so what’s the difference?  Relying on storage virtualization, RAID, or redundant array of inexpensive/independent disks, divides, replicates, and distributes data across the multiple drives.  JBOD, an acronym for just a bunch of disks, is precisely that—just a bunch of disks.  It has few of the merits of RAID, but there’s virtue in simplicity.

The individual disks of a JBOD array can each serve as a volume or they can be concatenated, or spanned, to form one single logical volume or LUN.  Whereas RAID demands that all drives be of similar capacity, JBOD drives can be of various sizes.

JBOD’s primary advantage is capacity utilization.  A JBOD array fully utilizes all the space on its drives.  A JBOD with four 300 gigabyte drives, for example, provides 1200 gigabytes of usable capacity.  In contrast, a similar RAID array will offer less than 1200 gigs of storage capacity because of the need to store redundant data.  How much space is needed for this redundancy depends on the particular RAID configuration.  RAID 1, for example, mirrors data on two or more drives, which means that only half the capacity of the disks is available for storage, the other half being used to store the duplicated copy.

As a result, JBOD is a cost-effective storage solution. JBOD controllers are less expensive than RAID controllers and you can mix and match disks while using every block for primary storage.

But JBODs have downsides.  The read/write operations of RAID can be much faster than those of JBODs.  With RAID, the data stream can be divided and stored on multiple disks concurrently, whereas JBODs store the data stream on one disk at a time.  RAID 0, for example, stripes data across two more or more disks to accelerate read/write operations.  Note, however, that it provides no redundancy.

More importantly, JBOD does not offer the redundancy of RAID.  If a disk is corrupted in a JBOD array, all your data is at risk, including what’s on the other drives.  With RAID, you can lose one or more disks and still preserve your data, depending on the configuration.

So when are JBODs useful?  If you have a lot of data to store, particularly if just temporarily, JBODs are an economical solution.  Make sure, however, that the data is not critical or you have an effective backup scheme in place.