A PCIe SSD (PCIe solid-state drive) is a high-speed expansion card that attaches a computer to its peripherals. PCIe, which stands for Peripheral Component Interconnect Express, is a serial expansion bus standard. PCIe slots can have different sizes, based on the number of bidirectional lanes that connect to it.
PCIe SSD storage is an alternative to a server-side flash deployment. PCIe serves as the underlying transport layer for data on graphics cards or add-in cards. PCIe SSDs integrate flash directly on a server motherboard. Each PCIe device connects to the host through its own serial link, eliminating the need to share a bus. The point-to-point architecture lowers latency and boosts data transfer speeds between a server and storage.
PCIe form factors and uses
Format specifications for PCIe-based devices are developed and maintained by the PCI Special Interest Group (PCI-SIG). PCIe 3.0, was released on November 2010. PCIe 4.0 was released in 2017 and doubles the bandwidth of the previous version. In May 2019, PCI-SIG announced the release of PCIe 5.0.
Support is emerging for PCIe SSDs designed for the non-volatile memory express (NVMe) specification. The NVMe protocol provides an optimized command set for accessing a PCIe SSD. NVMe exploits the parallelism of PCIe standards to accelerate performance.
The PCI-SIG also authored standards for M.2 SSDs, a small form factor designed for internally mounted expansion cards. The M.2 specification replaced the mSATA form factor. M.2 SSDs are equipped with four lanes of PCIe 3.0 bandwidth.
Prime PCIe flash use cases include applications with reading and write access measured in tens of microseconds. This reduced latency means faster response times for processing the large workloads associated with online transaction processing and data warehousing. Data centers use PCIe flash to meet the intensive input/output (I/O) requirements of these workloads.
Differences between PCIe SSD and SATA SSDs
As previously discussed, PCIe-attached SSDs avoid the bottlenecks associated with SATA or SAS-attached SSDs. The number of PCIe lanes per SSD determines the speed of data transfer. A 16-lane device built on the PCIe 3.0 specification can support approximately 32 gigabytes per second. By contrast, SSDs built with a SATA III controller provide a maximum transfer rate of about 600 megabytes per second.
The SATA v3.2 specification defines SATA Express connectors for host and device connectors that simultaneously support SATA and PCIe protocols. SATA SSDs have much better hardware capabilities, but they have worse relative performance. While it offers speeds of 600MB/s, it is not nearly as fast as speeds offered by PCIe SSDs.
If maximum performance for frequent file transfers is needed, PCIe is likely the most efficient option. If budget is a concern, SATA is much more cost-efficient as it tends to be the cheaper option.
PCIe SSD drawbacks
The PCIe multipurpose bus carries varied data to the processor. Despite its inherent performance benefits, PCIe SSDs have a higher cost per gigabyte than traditional SSDs.
The lack of standard storage commands is another drawback. PCIe SSD device makers are required to write and qualify a custom software driver for operating systems.
PCIe SSDs also tend to have much shorter battery life. However, if an individual is browsing the web, sending emails, or doing something that may be CPU or RAM intensive, they may not notice much of a difference between SATA and PCIe SSDs.