Results: A PCIe SSD's Random Performance
Random performance is another issue entirely. We already know that throughput ceilings aren't as much of a concern when it comes to moving around lots of small chunks of data. In fact SATA 6Gb/s is typically sufficient for heavy random workloads.
The Samsung XP941 employs AHCI, which has some inherent overhead that chokes the potential of solid-state storage. NVMe was designed to address this. However, Intel's NVMe driver isn't expected until the end of 2014. As a result, we have to accept that a PCIe-based SSD utilizing AHCI is probably going to demonstrate modest advantages, at best. How does the XP941 stack up in the two different connectors exposed by ASRock's Z97 Extreme6?
Random Read Performance
Given what we saw on the previous page, it'd be easy to assume that Samsung's XP941 is capable of massive transactional performance working with small random transfers. The truth is a matter of relativity.
Yes, 120,000 IOPS is an impressive result. But that number doesn't reflect the potential of Samsung's hardware the same way sequential transfers do. And yes, the four-lane Ultra M.2 slot does yield better results. However, the scaling isn't there to indicate that a two-lane interface attached to the PCH was really hamstrung, either.
Even more telling, the two- and four-lane interfaces track alongside the SATA 6Gb/s-based 840 Pro up until a queue depth of 16. Desktop workloads typically don't see that much concurrency, so the XP941 wouldn't confer much benefit.
Random Write Performance
This is mostly what I would have expected based on our previous work with PCIe-based SSDs utilizing AHCI. The SATA-attached 840 Pro takes top honors, even if it isn't the fastest SSD around. Samsung's XP941 falls flat connected to the two-lane M.2 slot. It fares better when we hook up with the four-lane Ultra M.2 interface, though not in any way that'd lead us to favor such a configuration over familiar SATA.
Bottom line: the random performance of a PCIe-based SSD is more pedestrian than the impressive sequential scores, largely due to AHCI. Still, if you stopped here and didn't look at any other benchmark, you might conclude that Samsung's XP941 is the greatest desktop-oriented SSD ever. But our testing in Iometer isn't necessarily indicative of how the drive behaves in the real world. We need to go into more depth.