SATA, SAS or Neither? SSD’s Get A Third Option
I recently wrote about solid state storage and its different form factor. Well, several major manufacturers have realized that solid state needs all the bandwidth it can get. Dell, IBM, EMC, Fujitsu and Intel have formed the SSD Form Factor Working Group bringing PCIe 3 to the same form factor that SATA and SAS use. Focusing on the same connector types and a 2.5” dive housing. I’m not sure how quickly it will make it’s way into the enterprise space but that is clearly it’s target. Reusing the physical form factor cuts down on manufacturing and R&D costs for all involved. They have an aggressive time scale for something like this. The specification hasn’t been published yet and I’ll take a deeper look into it when it becomes available. There are some key players missing though. HP and Seagate being the two in the enterprise space that give me pause. Both control a large segment of the storage space. On the controller side LSI is also absent. This could be a direct threat to their current market domination of the RAID controller chipset space if they aren’t on the ball.
Fusion-io got that early on and took a different route sticking with just PCIe to bypass the limitations of SAS/SATA and intermediate controllers. By going that route they opened up a whole other level of performance.
I asked David Flynn what he thought about the new standard. Fusion-io is a contributor to the working group.
It is quite validating that folks would be routing PCIe to the drive bays. For us it’s just another form factor that
we can easily support it.
Two things, though… First is that I believe it’s a hangover from the mechanical drive era to put such emphasis on form factors that allow easy servicing access. Solid state should not need to be serviced. It should be much more reliable than HDD’s. But, outside of Fusion-io failure rates for solid state is actually much worse than for mechanical disk drives.
The second point is that form-factor and even PCIe attachment isn’t really the key thing to higher performing, more reliable solid state. What makes the real difference is eliminating the embedded CPU bottleneck in the access path to the flash.
Fusion-io uses a memory controller approach to integrating flash. You don’t find CPU’s on DRAM modules. SSD’s (SATA or PCIe) from everyone else use embedded CPU’s and attach using storage controller methodologies.
In an upcoming post on my solid state storage series I will explore failure rates in detail. I do find it interesting that Fusion-io is one of the very few companies that have significantly higher error detection rates than a standard hard drive or other SSD’s, even enterprise branded SSD’s. Fusion-io claims 10^20 uncorrectable detectable error rate and 10^30 uncorrectable undetectable error rate. I have yet to see any hard disk or SSD with a rate better than 10^17. So, I agree with David about actually needing a form factor for ease of service if you build the device with enough error correction, which clearly you can with solid state.