PCIe SSD (PCIe solid-state drive)
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 them.
The key benefits of PCIe SSDs over the alternative server-based Serial ATA (SATA) drives include better compatibility, speed and storage capacity. PCIe SSDs are used for components like graphics cards and are ideal for users who need the fastest performance and lowest latency.
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 and a PCIe interface. 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
PCIe is one of four SSD form factors. In general, PCIe-based solid-state storage has better performance than SATA, serial-attached SCSI (SAS) or Fibre Channel SSDs.
Format specifications for PCIe-based devices are developed and maintained by the PCI Special Interest Group (PCI-SIG). PCIe 3.0 was released in November 2010. PCIe 4.0, which was released in 2017, doubled the bandwidth of the previous version. In May 2019, PCI-SIG announced the release of PCIe 5.0.
The PCIe 6.0 Specification, called Version 0.71, was released for members of PCI-SIG to review by July 2, 2021. The 6.0 specification is set for a full release by the end of the year. This latest bus standard doubles the data rate and bandwidth of the PCIe 5.0 specification.
PCIe 6.0 has a gigatransfer rate of 64 gigatransfers per second (GTps) with pulse amplitude modulation with 4 levels (PAM4) encoding. By comparison, PCIe 5.0 performs at 32 GTps using 128b/130b encoding; PCIe 4.0 performs at 16 GTps using 128b/130b encoding; and PCIe 3.0 has a gigatransfer rate of 32 GTps, also using 128b/130b encoding.
PCIe 6.0 also has low-latency Forward Error Correction to improve bandwidth, flow control unit used for encoding and backward compatibility with previous generations of PCIe-based technology.
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, which provides PCIe connectivity for small form factors -- 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 read 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 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 data transfer speed. A 16-lane device built on the PCIe 3.0 specification can support approximately 32 gigabytes per second (GBps). By contrast, SSDs built with a SATA III controller provide a maximum transfer rate of about 600 megabytes per second (MBps).
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 SATA SSDs offer speeds of 600 MBps, they are 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. But if budget is a concern, SATA is much more cost-efficient. PCIe SSDs cost more per gigabyte than SATA SSDs.
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 a much shorter battery life. However, if someone 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.
PCIe SSD cost and market
Pricing for PCIe SSDs differs by brand and available model sizes. For comparison, at the time of writing, the NVMe Gen3 PCIe SSD from SK Hynix Inc. cost $74.99 for a 500 GB drive, or $134.99 for a 1 terabyte (TB) drive. Likewise, the Samsung 980 PRO PCIe 4.0 NVMe is $79.99 for the 250 GB model, $119.99 for the 500 GB model, $197.00 for the 1 TB model and $429.99 for the 2 TB model.
Other example PCIe models include:
- Adata XPG Spectrix S40G. The Adata XPG Spectrix S40 PCIe M.2 SSD offers sequential read speeds up to 3500 MBps and write speeds up to 3000 MBps. It is available in 256 GB, 512 GB, 1 TB or 2 TB models.
- Seagate FireCuda 510. This M.2 NVMe SSD offers sequential read speeds up to 3400 MBps for both its 1 TB and 2 TB models. However, its write speeds differ for the 1 TB and 2 TB models, at 3050 and 3200 MBps, respectively.
- Crucial P5. This PCIe SSD delivers sequential read speeds up to 3400 MBps with write speeds up to 3000 MBps, save for the 250 GB model, which offers sequential read speeds up to 3400 MBps and write speeds up to 1400 MBps. This PCIe SSD is available in 250 GB, 500 GB, 1 TB or 2 TB models.
