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When it comes to determining the benefit of moving to PCI Express (PCIe) flash storage, there are a number of factors to consider. The most obvious is bus speed. Prior to the widespread adoption of SSDs, hard disk was the limiting factor. Today, most SSDs can handle a greater number of I/O operations, which now makes the storage controller a bottleneck. But moving to PCIe can help with this issue.
The SATA III specification allows data throughput at a rate of 6.0 Gbps. In contrast, many of the available PCIe-based storage products are based on the PCIe 2.0 standard, which has a throughput of 500 Mbps per lane. It is the number of lanes that dictate the overall available throughput. A 16-lane system, for example, can achieve speeds of up to 8 Gbps.
The significant difference in throughput goes a long way toward improving performance, but raw throughput is not the only consideration. Because the PCIe bus ties directly into the CPU, it eliminates the latency involved in passing instructions through a storage controller.
PCIe flash storage is a good choice for workloads that require high storage throughput and a high number of IOPS. However, the number of available PCIe slots limits the number of disks that can be installed, which in turn limits capacity and the total throughput that can be achieved across all drives. In theory, non-PCIe flash storage could offer better overall throughput if a system can accommodate significantly more SATA or SAS SSDs than PCIe SSDs (such as in a flash array).
Pros and cons of PCIe flash storage and memory channel storage
PCIe flash cache management and SSD power consumption
Dig Deeper on All-flash arrays
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