As the name suggests, PCIe-based flash storage devices plug right into one of the PCIe slots in a system. The PCIe bus is electrically very close to the memory and CPU in a server, which enables these flash systems to achieve extremely high throughput and I/O rates and enjoy very low levels of latency. Given that latency is enemy number one in a storage system, this is a tremendous benefit. Although electrical location is a benefit, there are other benefits as well. Due simply to the fact that the storage card plugs right into the PCIe bus, storage traffic can avoid controller-based roadblocks. This leave the PCI-e bus as one of the leading performance-based storage options on the market, with solutions that can meet the needs of even the most demanding applications while achieving very low latency figures.
Vendors that have developed PCIe storage devices generally enable their products to be leveraged in one of both of the following ways:
- As an accelerator (cache)
- As a performance storage tier
Many organizations have made significant investments in their legacy storage systems and, even if these systems are suffering from performance issues, they either can’t or don’t want to fully replace what they have. PCIe-based flash storage devices can be installed in host servers and act as a huge and fast cache in front of these legacy storage arrays, allowing companies to get a bit more life from these investments.
Also bear in mind that many of today’s standalone storage arrays are actually built using server hardware. PCIe cards can be leveraged as a local caching system in these arrays, accelerating all read and write activity in the array.
These flash cards can also be used for local storage; they don’t have to be relegated to caching duty. With very low latency and very high throughput, PCIe-based flash can be used for even the most demanding workloads. In general, PCIe cards leave SSDs far behind when it comes to raw performance. With very little in between the storage, CPU, and RAM – whereas SSDs suffer from abstraction in the form of SAS and SATA controllers – PCIe cards are far less hampered than SSDs.
The downside to PCIe-based flash storage devices is the relatively high cost when compared to other ways to leverage flash. As such, PCIe devices are generally use only when performance is paramount and there aren’t other ways to achieve performance goals.
When it comes to capacity, PCIe-based flash storage cards individually hold quite a lot of data, but systems have only a limited number of slots in which to add additional cards. This makes PCIe a challenge as a primary storage target, but, to be fair, that’s not generally its intended usage.