A SAS expander is a module that allows a SAS controller card to use more SAS/SATA drives than it would be able to use on its own, because of the limited number of SAS connectors on the card.

What do SAS cards do?

SAS Expanders are a newer storage technology that lets you maximize the storage capability of your SAS controller card. Many SAS controllers support up to 128 or more hard drives. ... Since many people are still unfamiliar with SAS Expansion, this site compares it to several storage technologies.

What is a SAS enclosure?

Our tower and rackmount SAS enclosures offer reliable, inexpensive external RAID or JBOD storage with hot-swap capability for both SAS and SATA drives. The enclosures on this page do not have a SAS expander, so you will get maximum bandwidth from your drives at a cheaper price point.