U.2 Introduction (AN44)
| Affected Products | All products |
Preface
This Application Note introduces the SFF-8639 (U.2) interface. The goal is to give an overview of the technology and hint on how to design-in this technology for customer carrier boards.
Terminology
| Term | Description |
|---|---|
| NVMe | Non-Volatile Memory Express |
| SSD | Solid State Drive |
| SAS | Serial-Attached SCSI |
| SATA | Serial ATA |
| SFF | Small Form Factor |
| OD | Open-Drain |
U.2 / SFF-8639 Introduction
Introduction
The U.2 specification (initially SFF-8639), which is released by the PCI-SIG group, describes a hardware interface that supports several SSD interface technologies.
This specification is used mostly for connecting high performance NVMe SSDs. For overview of the NVMe protocol, visit www.congatec.com and view the technote "NVMe support on congatec COMs and SBCs" in the restricted area of the website.
Backward Compatibility
One of the advantages of this specification is that it allows SATA, SAS and U.2 NVMe SSDs to be used on the same U.2 connector. This means that systems can be equipped with different types of SSD, depending on the demands of the system. In that way, the system can be scaled to perform different tasks, thereby improving the overall price efficiency of the design.
Advantages
U.2 SSDs are often used in data centers and server-related ecosystems. The SSD housing of a U.2 SSD is bigger and more ruggedized when compared to the bare PCB M.2 SSDs. This also allows U.2 devices to feature a bigger overall capacity.
U.2 devices can support hot-plug and hot-swap features. This capability allows new devices to be connected to the platform (hot-plug) or devices of the same type can be swapped out (hot-swap) while the system is up and running. The following conditions need to be met to support these features:
- The target SSD needs to support unplanned power loss.
- The BIOS of the congatec module you want to use needs PCIe hot-plug support.
U.2 SSDs often feature advanced power loss protection. This means that in a surprise power loss event, mandatory data transactions that have been cached can still be completed, making the SSD more robust to corruption in unstable power environments.
Note:
If you are unsure about hot-plug support on your congatec module, contact your FAE.
Connector Overview
This chapter gives a general overview of the U.2 connector. Sub-section 2.1 highlights the overall U.2 connector while sub-section 2.2 lists the pinout of all supported interfaces.