In doing enterprise storage systems, the selection of incorrect SAS cable would choke your whole system. Serial Attached SCSI cables are available in several connector types, at different speeds, and with different compatibility requirements, so to choose the appropriate cable, one needs to be aware of the differences between connector types. This reference guide dissects the most popular SAS cable and connector types, enabling you to make well-informed choices regarding your data center or server environment.
What Is SAS? (Quick Definition & Use Cases)
Serial Attached SCSI (SAS) is a point-to-point serial communication standard intended to provide high-performance communications in business settings. In contrast to parallel SCSI, SAS relies on serial communication to realize higher data rates and less cable bulk and electromagnetic interference. SAS technology only appears in servers, storage arrays, and data centers where reliability and speed are important.
SAS is usually used in enterprise-wide storage, disk arrays, tape libraries, and high-performance computing clusters. The protocol is compatible with both SAS and SATA devices and, therefore, can be used in mixed storage environments where mixed performance levels are required.
Why Cable & Connector Type Matters
SAS cable and connectors are the main factors that directly determine the performance, reliability, and further scalability of the system. There exist connector types with differing data transfer rates as low as 3 Gbps and as high as 24 Gbps per lane, and recent standards include even higher data transfer rates. Placing the wrong connectors that do not fit can cause a bottleneck and reduce the potential of your storage system.
Signal integrity over distance also depends on the quality of the cable. Shielding may be weak or improperly chosen, which may cause data errors, necessitating retransmission that impairs overall performance. Also, connector durability is important in the data center, where cables are often connected and disconnected in the course of maintenance or upgrades.
Common SAS Cable Types
SAS to SAS Straight-Through Cables
Typical SAS-to-SAS cables are device-to-device connections. These are generally identical connector unidirectional cables with both ends and can fully support full-duplex communications at rates of 12 Gbps46 per lane (SAS-3) or 24 Gbps46 per lane (SAS-4). They are typically attached to storage controllers with a disk enclosure, or to join two or more storage chassis.
Mini-SAS (SFF-8087) Cables
SFF-8087 mini-SAS connectors provide a smaller internal server connector. These 36-pin connectors allow 4 lanes of SAS traffic to be supported on one connector, eliminating cable clutter within the chassis. Internal connections Mini-SAS cables are often utilized between host bus adapters and backplanes, with 6 Gbps-per-lane (SAS-2) bandwidth.
Mini-SAS HD (SFF-8643 / SFF-8644) Cables
Mini-SAS HD (High Density) connectors are the next generation of Mini-SAS. SFF-8643 internal connectors and SFF-8644 external shielded connectors. Both are four-lane at faster speeds compared to standard Mini-SAS with support of SAS-3 (12 Gbps/lane) and faster standards. The higher pin density enables stronger signaling in the identical compact form factor.
Forward and Reverse Breakout Cables
Breakout cables work with one multi-lane SAS connector and divide it into several individual connections. Breakout cables are commonly used to connect a single SFF-8087 connector to four coupled SAS or SATA connectors (forward breakout) and many individual connections to one multi-lane connector (reverse breakout). These cables are flexible in nature and are used when mixing types of devices or when adaptors restrict the number to single connections.
SAS to SATA Breakout Cables
SAS breakout cables to SATA: SAS controllers can now be connected to SATA drives. As SAS can also be used in SATA devices (not the other way around), these cables will increase storage capacity by enabling SATA drives to be used cheaply in SAS systems. They usually re-purpose one SFF-8087 or SFF-8643 connector into four SATA connectors.
Common SAS Connector Types
SAS connectors come in different sizes, orientations, and usage. Standard SAS connectors (SFF-8482) are larger than SATA connectors and are intended to be used to connect individual devices. These are compatible with SATA power supply bases and SATA data communications with 15-pin and 29-pin connections.
Mini-SAS connectors are space-efficient in crowded spaces. In internal applications, the original Mini-SAS (SFF-8087) supports four lanes; external Mini-SAS (SFF-8088) supports four lanes with extra shielding that allows longer cable lengths. Angled versions of these connectors are used in tight chassis spaces.
Mini-SAS HD connectors are designed to be the densest, with up to four lanes, in an even smaller package compared to standard mini-SAS. The SFF-8643 internal and SFF-8644 external formats retrofit the faster SAS implementations of the future, but are compatible with suitable adapters.
How to Choose the Right Cable & Connector
When choosing the correct SAS cables, there are a number of factors to consider. Version compatibility is important at the interface level–check the compatibility of your cables with the SAS generation your devices need. SAS bus speeds are 3 Gbps/lane, 6 Gbps/lane, 12 Gbps/lane, and 24 Gbps/lane.
Signal integrity can be influenced by cable length; a shorter cable usually gives a better performance at higher speeds. In runs that are longer than the recommended distances, active cables with signal regeneration should be considered. Whether a shield is necessary depends on the electrically noisy environment or the proximity of cables to high-power equipment.
When choosing connector types, take into account future growth requirements. The mini-SAS HD connector is more future-proof than the standard Mini-SAS, and breakout cables are useful in mixed storage settings. Consider what kind of hot-swappable connections you need may be necessary for your application, which can affect connector selection and cable routing.
Quick Reference Comparison Table
| Connector Type | Use Case | Max Speed (per lane) | Lane Count | Form Factor |
| SFF-8482 (Standard SAS) | Individual devices | 24 Gbps | 1 | Large |
| SFF-8087 (Mini-SAS) | Internal multi-lane | 6 Gbps | 4 | Compact |
| SFF-8643 (Mini-SAS HD) | Internal multi-lane | 24 Gbps | 4 | Very compact |
| SFF-8644 (Mini-SAS HD External) | External multi-lane | 24 Gbps | 4 | Shielded |
| SFF-8088 (External Mini-SAS) | External multi-lane | 6 Gbps | 4 | Shielded |
FAQs
Can I use Mini-SAS HD with standard SAS devices? Yes, but you will have to use proper adapters or breakout cables. Mini-SAS HD may be used with standard SAS equipment using SFF-8643 to SFF-8087 adapters or breakout cables that convert the high-density connector to individual SAS connections.
Are SAS and SATA cables interchangeable? SAS controllers are able to communicate with SATA devices over the correct cables, but SATA controllers are not able to directly control SAS devices. The connectors might be similar, but SAS cables also have more signaling capacity that is not found in SATA cables.
What’s the difference between forward and reverse breakout cables? These forward breakout cables divide a single multi-lane connector into several single connections (one SFF-8087 to four SAS/SATA). Multi-connection reversible breakout cables are used to connect many single connections into a single multi-lane connector (four SAS/SATA to one SFF-8087). Select according to your relationship direction requirements.
Do I need different cables for different SAS speeds? Fast SAS implementations have cables with more rigid electrical requirements. Although physically a SAS-2 cable can be used to connect to a SAS-3 system, it might not fully support the speeds or may create errors. Cables you use must be rated to match the highest speed of your system.
Conclusion
It is important to choose SAS cables and connectors to create high-performance storage systems that are reliable. Whenever it comes to meeting the speed requirements, comprehending the distinctions between the Mini-SAS, Mini-SAS HD, and the standard SAS connectors can help ensure compatibility. Look at what you need now and what you might need in the future, and make it a habit to confirm that cable specifications fit your performance needs in your system.
