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SSDs In RAID: A Performance Scaling Analysis

SATA Bottleneck: 3 Gb/s Is Not Enough

We decided to use the LSI 9280-24i4e RAID controller in order to investigate the SSD RAID scalability without restrictions. The 24 SATA and four SAS ports of the LSI controller are enough for the professional focus of this article, as is the eight-lane PCI Express 2.0 interface sporting a theoretical data rate of 4000 MB/s. The bandwidth per port is 6 Gb/s, raising the speed limit of the old 3 Gb/s SATA.

In addition to the controller, we also installed the FastPath software from LSI, which claims to significantly increase the I/O access speed of the connected SSDs. LSI is not very outspoken about just how this works, cryptically mentioning special low-level access to the SSDs. But it works with any flash-based system and maximizes write and read performance. LSI wants to achieve a 2.5-fold increase in write performance compared to an unaccelerated system, and twice the read performance.