Three PCI Express-Based SSDs: When SATA 6 Gb/s Is Too Slow

When it comes time to hunt down the ultimate in storage performance, you simply cannot settle for standard SSDs. Instead, look to PCI Express-based drives that circumvent the limitations of SATA. We have products from Fusion-io, LSI, and OCZ on the bench.

SSD vendors are all in the middle of transitioning from 3 Gb/s to 6 Gb/s interface speeds, which effectively doubles the available interface speed on solid state drives. But if you think that achieving 500 MB/s is fast you should think again. Flash-based storage can be made to move data much faster than that once it is no longer limited by Serial ATA. Today we're comparing the latest offerings from Fusion-io, LSI, and OCZ to figure out who makes the fastest solid state drive available today. To do that, we must say goodbye to SATA and hello to PCI Express!

The idea behind the four products we compare in this article is simple: their creators want to maximize throughput, I/O performance, or both. Cost ends up being secondary on this venture. Fusion-io, LSI Corporation, and OCZ Technology all share a common opinion of the Serial ATA interface. Mainly, it's inadequate for a true high-performance product, as the bandwidth is limited to less than 600 MB/s on SATA 6Gb/s. Therefore, all of the products in this roundup center on PCI Express, which directly attaches flash storage to the fastest available system interface. With that said, this doesn’t mean that SATA cannot be used at all. In fact, both LSI and OCZ employ SATA to connect flash memory to their solutions internally.

The individual approaches on how to procure maximum performance differ a lot. While LSI and OCZ create cards that employ RAID-based configurations using multiple controllers attached to dedicated NAND flash, Fusion-io is the first and only firm to provide a direct PCI Express storage solution that doesn’t utilize an internal storage interface like SATA. Therefore, we decided to put the LSI WarpDrive and OCZ’s Ibis up against the ioDrive and the ioXtreme by Fusion-io.

As always, different implementations have their own unique pros and cons. As mentioned, LSI and OCZ access conventional RAID and storage controllers to create powerful devices, while Fusion-io created new silicon to minimize the number of interfaces that have to be involved. The latter appears to be the most elegant solution. But it's still not bootable. That might not be very important in enterprise environments, where lots of capacity and high performance is used to accelerate I/O-intensive workloads. It is a problem in the enthusiast space, though.

Be that as it may, in the end, we’re interested in understanding how each product is designed and how it works. And what matters most are the benchmark results, right? Let’s look at the ioDrive (160 GB) and ioXtreme (80 GB) by Fusion-io, the LSI WarpDrive Accelerator Card SLP-300 (300 GB), and OCZ's Ibis. The Ibis is technically very similar to the RevoDrive X2 that Chris reviewed in January 2011 (Ed.: And, in fact, I took an early look at the Ibis in OCZ's HSDL: A New Storage Link For Super-Fast SSDs, too).

Before we dive too deeply into this comparison, which may strike some readers as imbalanced based on the pricing of each product, it is important to consider the markets addressed by high-end PCI Express-based SSDs. The solutions sold by Fusion-io and LSI are clearly geared towards an enterprise audience. Their design, components, firmware, support and pricing are totally different from OCZ's Ibis and its more enthusiast/workstation-oriented specifications. The Ibis just happens to interface via PCI Express as well. To make a long story short, please don't take this review as a shootout, but as a look at different concepts and options. We think the conclusion reflects unique considerations for each dissimilar piece of hardware.