SAS
What Is SAS?
SAS stands for Serial Attached SCSI. It is an enterprise storage interface that carries SCSI commands over a serial connection and is commonly used with server hard drives, SSDs, RAID controllers, HBAs, storage backplanes and external storage systems.
SAS was designed for environments that value reliability, scalability, multi-device connectivity and enterprise storage features. SAS infrastructure can support large drive topologies through expanders and can also provide dual-path connectivity when supported by the drive and storage system.
SAS at a Glance
SAS Speeds & Generations
SAS has evolved through multiple generations, increasing the signaling rate available on each SAS lane.
| Generation | Signaling Rate | Approx. Raw Byte Rate Per Lane | Common Context |
|---|---|---|---|
| SAS-1 | 3 Gb/s | Approx. 300 MB/s | Legacy enterprise storage |
| SAS-2 | 6 Gb/s | Approx. 600 MB/s | Older enterprise servers |
| SAS-3 | 12 Gb/s | Approx. 1.2 GB/s | Common enterprise SAS infrastructure |
| SAS-4 | 22.5 Gb/s | Higher than 12 Gb/s SAS | Newer high-performance SAS infrastructure |
Interface signaling rate is not the same as end-to-end storage throughput. Drive media, controller performance, lane width, protocol overhead and workload affect real-world results.
SAS HDD vs SAS SSD
SAS Hard Drives
SAS hard drives have traditionally been used for enterprise workloads requiring reliable server storage, higher rotational speeds and SAS-specific connectivity. Common enterprise SAS HDD speeds include 10,000 RPM and 15,000 RPM, although large-capacity SAS HDDs can also use lower spindle speeds.
SAS Solid-State Drives
SAS SSDs combine flash storage with the SAS interface and enterprise storage features. They can provide much lower latency and substantially higher random I/O performance than SAS hard drives while retaining compatibility with SAS-oriented storage platforms.
What Is Dual-Port SAS?
Many SAS devices support two independent ports. In storage architectures designed for multipath access, those ports can provide separate communication paths between a drive and controllers or hosts.
Dual-port connectivity can improve path redundancy and is one reason SAS is widely used in enterprise storage shelves, shared storage systems and high-availability designs.
Two Paths to the Same Drive
What Is a SAS Expander?
A SAS expander allows a SAS controller or HBA to communicate with more storage devices than could be attached using only its direct physical ports. Expanders are common in enterprise server backplanes, JBOD enclosures and large storage systems.
Large SAS topologies can include initiators, expanders and many target devices. Available bandwidth is shared across the topology, so controller links, expander design, lane count and workload all matter when planning performance.
SAS vs SATA vs NVMe
SAS
Enterprise storage interface with scalable topologies, optional dual-port connectivity and mature RAID/HBA support.
SATA
Cost-effective interface commonly used for capacity HDDs and SATA SSDs in servers, workstations and general-purpose storage.
NVMe
Flash-optimized storage protocol using PCI Express for high bandwidth, deep queues and low protocol latency.
Can a SAS Controller Use SATA Drives?
Many SAS controllers, HBAs and SAS backplanes can communicate with SATA drives. This allows compatible enterprise servers to use SATA storage on SAS-oriented infrastructure.
Support must still be verified for the specific controller, server, backplane, firmware and drive configuration.
A SATA Controller Cannot Normally Use a SAS Drive
SAS infrastructure is designed to support SAS protocol and can often support SATA devices. A SATA-only controller does not understand the SAS protocol and therefore cannot normally operate a SAS drive.
Where Does SAS Fit in Enterprise Storage?
SAS is particularly well suited to server and storage platforms requiring mature RAID support, scalable drive connectivity, enterprise backplanes, dual-path storage architectures and predictable compatibility with established storage controllers.
Choosing SAS Storage
Match the drive, controller and backplane to the workload and server platform.
SAS Drives and RAID
SAS HDDs and SSDs are commonly deployed behind enterprise RAID controllers. RAID level, drive count, drive capacity, controller cache, hot-spare strategy and workload all affect usable capacity, performance and fault tolerance.
SAS FAQ
What does SAS stand for?
SAS stands for Serial Attached SCSI, an enterprise storage interface used for HDDs, SSDs, RAID controllers, HBAs and storage enclosures.
Is SAS faster than SATA?
SAS interfaces can provide higher per-lane signaling rates than SATA, but actual storage performance also depends on the drive, controller and workload.
Can SAS controllers use SATA drives?
Many SAS controllers and backplanes support compatible SATA drives, but support should always be verified for the specific server and controller.
Can a SATA controller use a SAS drive?
Normally no. SATA-only controllers do not support the SAS protocol required by SAS drives.
What is dual-port SAS?
Dual-port SAS provides two independent drive ports that can be used for redundant storage paths in compatible architectures.
Is NVMe faster than SAS?
NVMe can provide substantially higher bandwidth and lower protocol latency because it uses PCI Express and was designed specifically for solid-state storage.