A SAS drive is a hard drive or solid-state drive that uses the Serial Attached SCSI (SAS) interface, an enterprise storage connection built for servers and storage arrays. SAS drives offer higher link speeds, dual-port redundancy, deeper command queues and longer cable runs than SATA drives, which is why data centers use them for workloads that must stay fast and available.
Key takeaways
- SAS stands for Serial Attached SCSI and is the enterprise counterpart of SATA.
- SAS link speeds have grown from 3 Gb/s (SAS-1) to 22.5 Gb/s (SAS-4, marketed as 24G SAS).
- SAS is full duplex and many SAS drives have two ports, so one failed path does not cut off the drive.
- A SAS backplane can accept SATA drives, but a SATA controller cannot use SAS drives.
- Choose SAS for busy databases, virtualization and arrays. Choose SATA for bulk, cost-sensitive capacity.
What is a SAS drive?
A SAS drive is a storage device that connects through the Serial Attached SCSI interface, which carries the SCSI command set over a point-to-point serial link. SAS replaced the older parallel SCSI standard. You will find SAS drives in rack servers, SAN and NAS arrays and disk shelves, as spinning hard drives at 10,000 or 15,000 RPM, as nearline 7,200 RPM models, and as SAS SSDs.
How fast is a SAS drive?
A SAS drive runs at the speed of its SAS generation: 3 Gb/s for SAS-1, 6 Gb/s for SAS-2, 12 Gb/s for SAS-3 and 22.5 Gb/s for SAS-4. The chart compares the link speed of each generation. A mechanical drive rarely fills the whole link, but SAS SSDs and multi-drive arrays can use the extra headroom.
SAS vs SATA: what is the difference?
SAS is built for enterprise reliability and parallel workloads, while SATA is built for lower cost and larger capacity per dollar. The table lists the main differences.
| Feature | SAS | SATA |
|---|---|---|
| Top link speed | 22.5 Gb/s (SAS-4) | 6 Gb/s (SATA III) |
| Duplex | Full duplex | Half duplex |
| Ports | Often dual-port for redundant paths | Single port |
| Command queue | Deep queue, up to 256 commands | NCQ, up to 32 commands |
| Cable length | Typically up to 10 m | Typically 1 m |
| Typical cost | Higher | Lower |
| Best for | Databases, virtualization, arrays | Backup, archive, desktops |
What are the benefits of SAS drives?
The main benefits of SAS drives are speed under load, redundancy and scale. In practice that means:
- Dual-port redundancy. A drive can connect to two controllers, so a failed cable or controller does not take it offline. This supports the designs described in our guide to high availability.
- Full duplex and deep queues. Reads and writes can flow at the same time, which helps busy multi-user workloads.
- Scalability. SAS expanders let one controller address thousands of drives in a storage shelf.
- Enterprise reliability features. SAS drives typically carry stronger error handling and longer warranties than consumer drives.
Can you mix SAS and SATA drives?
You can use SATA drives on a SAS backplane or controller, but you cannot use SAS drives on a SATA-only controller. The SAS connector is designed so SATA drives fit, which lets you mix both in one chassis. A SATA drive in that setup still runs at SATA speed and without dual-port support. Do not mix them inside one RAID group, because the slower drive sets the pace.
Which workloads should use SAS?
Use SAS for workloads that need steady performance under many simultaneous requests and that cannot tolerate path failures. Good fits include:
- Database servers and transaction processing.
- Virtualization hosts and shared storage for virtual machines.
- Storage arrays that use RAID, as in our explainers on RAID 1 mirroring and RAID 50.
- Tiered storage, where fast SAS drives hold hot data and cheaper drives hold the rest, as described in hierarchical storage management.
For large, rarely read data such as backups and archives, nearline SATA or nearline SAS drives usually give a better cost per terabyte.
How do you choose and install a SAS drive?
To choose a SAS drive, match its generation, form factor, capacity and interface to your controller and backplane. Follow these steps:
- Check the controller or HBA SAS generation and make sure it supports the drive speed.
- Pick the form factor, such as 2.5 inch or 3.5 inch, to fit the drive bays.
- Decide between hard drive and SAS SSD based on workload and budget.
- Buy drives from the vendor compatibility list when the server vendor locks firmware.
- Install the drive in the carrier, insert it into the bay and let the controller detect it.
- Create or rebuild the RAID set, then test failover and monitor drive health.
If you are moving drives between racks, our data center migration checklist helps you plan the work.
Frequently asked questions
What does SAS stand for?
SAS stands for Serial Attached SCSI. It is a serial interface that carries SCSI commands between a controller and storage devices.
Is SAS faster than SATA?
Yes. SAS-3 runs at 12 Gb/s and SAS-4 at 22.5 Gb/s, while SATA III tops out at 6 Gb/s. SAS also handles many simultaneous requests better because it is full duplex with deeper queues.
Can I plug a SAS drive into a SATA port?
No. SAS drives need a SAS controller or backplane. SATA drives, however, work on SAS ports.
Are SAS drives still used?
Yes, mainly in enterprise servers and storage arrays. Many new builds also use NVMe SSDs for the fastest tier, while SAS stays common for shared storage and mixed workloads.
What is the difference between a SAS HDD and a SAS SSD?
Both use the SAS interface. A SAS HDD stores data on spinning platters and offers high capacity, while a SAS SSD uses flash memory for much lower latency. Our guide to common SSD performance issues covers flash problems.
Conclusion
A SAS drive gives you enterprise speed, dual-port redundancy and room to scale, at a higher cost than SATA. Use SAS where uptime and steady performance matter, use SATA for bulk capacity, and match every drive to your controller generation before you buy.
