4x4 Ports: Multi-Lane Technology, Enclosures, Connections
SAS supports a variety of different cables. SFF-8482 is the internal connector for individual drives, while SFF-8087 connectors are used on host adapter cards internally; SFF-8088 is the external version. Both are also known as mini-SAS, and they merge four individual ports into one connector.
The cards we're reviewing in this article all offer four internal SFF-8087 ports, for up to 16 clients. Adaptec and Areca also offer an additional external port; SFF-8484 is used to condense four ports into one connection internally.
Multi-lane cables and connectors are used to connect SAS enclosures and appliances to host adapters. This is often done regardless of the actual number of drives used, meaning that a single multi-lane connection may be used to operate anything from a single drive to 16, 24, or even more drives, depending on the enclosure configuration. The four ports available per multi-lane connection add up to 1,200 MB/s of bandwidth, which is sufficient to operate high-performance drive arrays.
SAS storage enclosures are used for a simple reason: they’re easier to manage than storage that is installed directly into servers. Since enterprise systems are always mounted into 19” racks, it makes a lot of sense to add SAS enclosures as you need them. But you don’t have to go for enclosures: it is still possible to hook up individual drives to SAS adapters directly. All you need are the appropriate cables, which you typically have to purchase separately.
SAS devices are often dual-ported, allowing controllers to establish two physical connections for the sake of redundancy, or to double the interface bandwidth. A single SAS connection runs at 300 MB/s today, with 600 MB/s available later this year. Keep in mind that this bandwidth is not necessarily relevant when connecting individual drives, but it certainly matters when attaching multiple drive arrays to host adapters via multi-lane cables.