SAS vs SATA vs NVMe: Drive Interfaces, and Why Servers Use SAS

When choosing drive interfaces for your homelab or server, understanding the differences between SAS, SATA, and NVMe is crucial. This guide explains each interface type and why servers often use SAS.

Overview

The three primary ways drives communicate with computers are:

• SATA: The consumer standard since around 2003, offering a maximum speed of 6 Gbps (SATA III), real-world speeds of about 550 MB/s. It uses one connection per drive and is half-duplex. SATA is cheap, universal, and suitable for HDDs and budget SSDs.
• SAS: The datacenter cousin to SATA, offering a maximum speed of 12 Gbps (with the newest generation at 24 Gbps), full duplex, deeper command queues, dual-port drives, longer cable runs, and expanders. SAS controllers can also run SATA drives, but not vice versa. SAS is built for enterprise use with better error recovery.
• NVMe: Not a cable standard but a protocol that speaks PCIe directly, bypassing the SATA/SAS controller stack. NVMe offers high speeds, especially in M.2 form factors (gen4 ~7000 MB/s) and enterprise U.2/U.3 drives (2.5-inch drives with PCIe, hot swap, huge endurance). NVMe has lower latency compared to SATA.

Why Servers Use SAS

Servers historically used SAS because of its reliability features such as dual-port drives and better error handling. SAS also supports expanders for 24-90 bay chassis, making it suitable for large-scale storage solutions. However, new all-flash servers are increasingly opting for NVMe due to the bottleneck created by the SAS controller.

Homelab Guidance

HDD Arrays

For home lab use with HDD arrays:

• SATA NAS drives: Suitable for most home lab needs.
• Used enterprise SAS drives: A cost-effective option if you have a suitable controller (e.g., an LSI HBA in IT mode, ~$40 used), which is ideal for 8+ drive setups. These drives are quieter and use less power compared to consumer SSDs but come with the tradeoff of increased noise and power consumption.

Boot/OS/Virtual Machine Storage

For booting your OS or running virtual machines:

• NVMe M.2: Nearly as cost-effective as SATA SSDs now, offering significantly faster speeds.
• SATA SSDs: Still a good choice for budget considerations but slower than NVMe.

The SFF-8087/8643 Cable Alphabet

Understanding the cable types is essential:

• Mini-SAS cables: Carry 4 lanes each and are used to connect HBAs to backplanes.
• Breakout cables: Convert one port into multiple SATA plugs, useful for expanding connections.

Gotcha: M.2 Slot Compatibility

An important note: An M.2 slot can support both SATA and NVMe devices, so always check the compatibility before purchasing a fast M.2 stick for an older motherboard.

By understanding these differences, you can make informed decisions when building or upgrading your home lab or server setup.