Understanding SAS Expanders: A Beginner's Guide
Have you ever found yourself staring at a server, knowing you need more storage but dreading the cost and complexity of adding more host bus adapters? Running out of space is a common problem, and thankfully, there's a neat solution you might not have considered: SAS expanders.
A SAS (Serial Attached SCSI) expander is a hardware device that significantly increases the number of SAS and SATA drives connected to a single SAS port on your host controller. Think of it as a multiplier for your storage connectivity. In this post, we'll dive into what SAS expanders are, how they work to extend your server's capabilities, and the basic considerations for using them effectively. Whether building a high-density storage solution or simply trying to maximise your existing infrastructure, understanding SAS expanders can unlock new possibilities for your data storage needs.
What is a SAS Expander?
Serial Attached SCSI, otherwise known as SAS, is a high-speed data transfer interface commonly used in data storage solutions. It's a successor to the parallel SCSI, offering improved speed and flexibility. SAS connects hard drives and other storage devices to a server or workstation.
A SAS expander is a hardware device that significantly extends the connectivity of a SAS infrastructure. It lets you connect more SAS or SATA Serial ATA drives to a single SAS port on a host controller. Think of it like a USB hub for your hard drives. Just as a USB hub takes one USB port and expands it to multiple ports for connecting various USB devices, an SAS expander takes one SAS port and expands it to support numerous SAS/SATA drives.
While different types of SAS expanders are available, their core function remains the same: multiplying the number of storage devices connected to a SAS system.
How Does a SAS Expander Work?
Using a SAS expander that you connect to your server motherboard, you can use your server PCIE lanes and connectivity in another chassis. This can allow you to spread out large and bulk drives more efficiently when building storage servers or infrastructure, allowing for more efficient redundancy and cooling setups at scale. The following diagram demonstrates the connectivity achieved using a Sas expander car to connect drives connected in a secondary chassis with their independent cooling and power.
Using SAS Expanders: Basic Considerations
SAS expanders are commonly employed in scenarios where increased storage capacity is essential. Typical use cases include expanding the storage capacity of servers, creating large RAID (Redundant Array of Independent Disks) arrays for enhanced data protection and performance, and building high-density storage solutions.
1. Compatibility is Key
Compatibility is paramount when integrating a SAS expander into your system. It's crucial to ensure that the expander is fully compatible with your SAS host controller and the SAS or SATA drives you intend to connect. Incompatibility can lead to a variety of issues, including performance bottlenecks or even a failure to recognize the connected drives.
2. Essential Setup Steps
Basic setup considerations also play a vital role in ensuring proper functionality. Adequate power must be supplied to the expander to support all connected drives. Proper cabling is essential for reliable data transfer, and the correct cables must be used. Furthermore, some expanders may require an initial configuration process to set up the SAS topology and ensure that all drives are correctly recognized by the system.
3. Popular SAS Expander Manufacturers
Several manufacturers offer SAS expander cards. Broadcom (formerly LSI) SAS expanders are very common and widely used in many systems; an example is the Broadcom/LSI SAS9217-4i4e. Microsemi (formerly Adaptec) also produces reputable SAS expanders. These examples are for informational purposes only and do not represent an endorsement of any specific brand.
4. Key Selection Factors
When selecting a SAS expander, several factors warrant careful consideration. The number of ports (both internal and external) determines the number of drives you can connect. The SAS speed (6Gbps, 12Gbps, or faster) impacts the potential data transfer rate. Power requirements must be assessed to ensure your system can adequately supply the necessary power. The expander's form factor should also be considered to ensure it fits properly within your server or system enclosure.
5. Potential Performance Implications
Finally, potential performance considerations must be taken into account. While SAS expanders significantly increase connectivity, they can also introduce bandwidth limitations if many drives are accessed simultaneously. The aggregate bandwidth of the SAS expander must be sufficient to handle the combined data throughput of all connected drives to avoid performance bottlenecks.
Wrapping Up
In conclusion, SAS expanders are valuable tools for expanding storage capacity and connectivity in SAS-based systems. They enable the connection of numerous SAS/SATA drives to a single host controller port, offering increased storage capacity, enhanced flexibility, and often a more cost-effective solution compared to using multiple host bus adapters.
By considering compatibility, setup requirements, key selection factors, and potential performance implications, you can effectively leverage SAS expanders to build robust and efficient storage solutions tailored to your needs. We encourage you to explore specific SAS expander models further to better understand their unique features and applications.
Check out our range of HBA cards and adapters at the link HERE to find the perfect solution for your storage needs!
You can also check some of our other posts if you want to learn more about scaling your storage in the homelab:
