UK What SAS and SATA are
SAS (Serial Attached SCSI) and SATA (Serial ATA) are the two serial interfaces that connect hard drives and SSDs to a computer. Both replaced older parallel buses in the early 2000s, and both use similar-looking connectors, but they come from different families. SAS carries the SCSI command set used in servers and storage arrays, and is developed by the INCITS T10 committee. SATA carries the ATA command set used in PCs, and is developed by the Serial ATA International Organization (SATA-IO).
In practice, SATA is the everyday interface on desktops, laptops, embedded boards and industrial PCs. SAS sits behind RAID controllers and host bus adapters (HBAs) in servers and storage enclosures, where uptime and many drives per controller matter more than cost.
SAS vs SATA side by side
The headline difference is speed, but the features that matter most in a server are dual porting and full duplex. The table compares current versions of each.
| Feature | SAS | SATA |
|---|---|---|
| Line rate | 12 Gb/s (SAS-3), 22.5 Gb/s (24G SAS) | 6 Gb/s (SATA III) |
| Duplex | Full duplex: reads and writes at the same time | Half duplex: one direction at a time |
| Ports per drive | Two, so a drive can reach two controllers | One |
| Command queue | Hundreds of commands per drive | 32 commands (NCQ) |
| Cable length | Up to around 10 m | Around 1 m internal |
| Drives per controller | Many, through expanders | One per port, more with port multipliers |
| Typical drives | 10K and 15K rpm hard drives, enterprise SSDs | 7,200 rpm hard drives, SATA SSDs |
Speed figures are interface limits. A single SATA SSD already saturates its 6 Gb/s link, while one SAS SSD can use most of a 12 Gb/s link, and hard drives of either kind are limited by their mechanics long before the interface.
Why servers use SAS
SAS was designed for systems that cannot stop. Its extra features cost more in the drive and the controller, which is why it is rarely found outside servers and storage enclosures.
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Dual porting. Each SAS drive has two independent ports, so two controllers can reach it. If one controller or cable fails, the other carries on, which is the basis of high-availability storage.
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Expanders. SAS expanders let one controller address dozens or hundreds of drives across backplanes and external enclosures.
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Error handling and reliability. Enterprise SAS drives are typically specified at one unrecoverable read error per 1016 bits, against 1014 to 1015 for SATA drives, and their firmware is tuned for RAID error recovery.
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Mixed workloads. Full duplex and a deep command queue help when many virtual machines or databases hit the same drives at once.
Mixing SAS and SATA drives
SAS was designed to be compatible with SATA in one direction. A SAS controller or backplane accepts SATA drives and talks to them using the SATA protocol. A SATA controller cannot run a SAS drive: the SAS drive connector fills the gap between the data and power sections, so a SATA cable will not even fit. Mixing SAS and SATA drives on one controller is possible, but keep each RAID array to one type, because the slower or less reliable drive sets the pace for the whole set.
Many current server and rugged backplanes use the U.2 connector, which can carry SAS, SATA or NVMe depending on how the backplane is wired. Several of our rugged computers take two, four or eight hot-swap U.2 NVMe drives in front bays, which gives array-class speed in a fanless chassis without a SAS controller. Others carry hot-swap SATA bays for drives that are swapped out at the end of each shift or mission.
Which to choose for an edge or industrial system
Most industrial PCs, embedded boards and edge computers use SATA and NVMe, not SAS. They usually carry a few drives, often run without a RAID controller, and sit where an add-in SAS HBA would add heat and power for little gain. SAS appears where the edge system is really a server: multi-drive storage nodes and rack mount servers with RAID controllers and many front bays.
If you are choosing between them, start from the drive count and the uptime target. One to four drives with software RAID, or a single boot drive, points to SATA or NVMe. A large array that must survive a controller failure points to SAS or dual-ported NVMe, built around server motherboards with the PCIe lanes to feed the controller.
Quick answers on SAS vs SATA
SAS and SATA: common questions
Is SAS faster than SATA?
Yes, at the interface. SAS-3 runs at 12 Gb/s and 24G SAS at 22.5 Gb/s, against 6 Gb/s for SATA III, and SAS is full duplex. A 7,200 rpm hard drive performs much the same on either, because the disk is the limit.
Can SAS drives work on SATA?
No. A SATA controller cannot drive a SAS disk, and the SAS connector is shaped so a SATA cable will not plug in. It works the other way: SATA drives run on SAS controllers.
Is SAS better than SATA?
For servers, usually. Dual porting, expanders and stricter error handling suit high-availability storage. For PCs, embedded systems and most edge computers, SATA or NVMe is simpler and cheaper and does the job.
Why do SAS drives cost more?
They carry more hardware. Dual-port electronics, enterprise-grade components, longer validation and smaller production volumes all add cost, and SAS also needs a controller that most motherboards do not include.
Is NVMe replacing SAS?
For SSDs, largely. NVMe over PCIe outperforms 12 Gb/s SAS, and U.2 and E3.S bays now carry NVMe in many new servers. SAS remains common for high-capacity hard drives and existing storage arrays.
We build every server and industrial PC with its drives, controller and RAID set fitted as standard, matched to the drive count, uptime target and temperature range of the installation.