Backplanes Basics

These slots conceal a high-quality SCSI backplane.

The term "backplane" is taken from SCSI. If you dissect the word you get a "back wall board" that merges the signals of all SCSI drives to connect one port to the bus cable rather than all individual drives. That reduces the jumble in the case and saves you the expense of buying pricey SCSI cables with up to eight connectors.

The practical advantage in operation is that you can remove individual drives from the system to the exclusion of others without interrupting server operation, and then insert a replacement drive. The time saved is obvious. If the operating system is run on an intelligent RAID hard-drive setup, operation can continue even if one drive crashes.

That's why backplanes also have an additional logic for suppressing voltage fluctuation to the greatest possible degree while a drive is being inserted or removed during operation (hot swapping).

Today the term backplane has also spread to SATA, although it is not really a classic backplane anymore, because the power is usually drawn directly from the power supply - thus, fluctuations depend on the quality of the power supply. Because of this, manufacturers of the three devices reviewed here make references to "enclosures".

The devices we tested were all suitable for a maximum of four drives and took up a total of three free 5.25" slots.

On the right is the board, the actual "backplane," which holds the SCSI ports for the SCSI drives with SCA interface. The connection to the host adapter is made with a regular 68 pin SCSI cable.