Results: Tom's Hardware Storage Bench v.1.0
Most of the Z97 Express-based boards you see will include the chipset's six SATA 6Gb/s ports. Some will also feature the PCH-attached M.2 slot we're testing today. And others will expose SATA Express. The Z97 Extreme6's most prominent differentiator is that x4 M.2 slot wired into Intel's LGA 1150 interface, though.
We aren't testing SATA Express yet, and that's for good reason. Most of the first drives will be AHCI-based. And that means they won't be much different from SSDs like SanDisk's A110, which we've already reviewed. As you look at the benchmark results for Samsung's XP941 on a two-lane M.2 interface, consider that a stand-in for SATA Express. The story only really gets interesting once NVMe support is added.
Storage Bench v1.0 (Background Info)
Our Storage Bench incorporates all of the I/O from a trace recorded over two weeks. The process of replaying this sequence to capture performance gives us a bunch of numbers that aren't really intuitive at first glance. Most idle time gets expunged, leaving only the time that each benchmarked drive is actually busy working on host commands. So, by taking the ratio of that busy time and the the amount of data exchanged during the trace, we arrive at an average data rate (in MB/s) metric we can use to compare drives.
It's not quite a perfect system. The original trace captures the TRIM command in transit, but since the trace is played on a drive without a file system, TRIM wouldn't work even if it were sent during the trace replay (which, sadly, it isn't). Still, trace testing is a great way to capture periods of actual storage activity, a great companion to synthetic testing like Iometer.
Average Data Rate
The Storage Bench trace generates more than 140 GB worth of writes during testing. Obviously, this tends to penalize drives smaller than 180 GB and reward those with more than 256 GB of capacity.
In this abbreviated performance analysis, we cut out a lot of the SATA 6Gb/s drives you're used to seeing in our charts. The results are generated under Windows 8.1, whereas our library of data is mostly based on Windows 7. We had some issues using the Ultra M.2 slot under that older operating system, though. Previously, Windows 7 used MSAHCI.SYS. Windows 8 uses the STORAHCI.SYS driver for PCIe-based SSDs. We found the newer driver serves up less consistent latency and service times, dramatically affecting storage performance. Meanwhile, Samsung's 840 Pro is controlled by Intel's RST driver, so it doesn't care either way. For reference, we explored the implications of both drivers in Plextor M6e 256 GB PCI Express SSD Review: M.2 For Your Desktop.
Samsung's XP941 in ASRock's unique Ultra M.2 slot posts the highest average data rate, followed by the same SSD in a PCH-attached M.2 slot. The SATA 6Gb/s 840 Pro takes third place, managing to lead SanDisk's A110, which also connects to the PCI Express bus. Plextor's M6e finishes in last place.
But service times are also important in a test like this one.
This is a plot of read and write service times. Reads are on the x-axis; write service times are on the y-axis. These numbers are far more important than average data rates on their one. And using both metrics, we can make far more precise observations about drive performance with real workloads.
As always, down and left is where you want to be. Numbers closer to the origin indicate better performance.
Don't compare these results to any of our previous reviews. Again, they were generated under Windows 8.1, which is less kind to PCIe-attached solid-state storage due to a reliance on the operating system's STORAHCI driver. I'm expecting the picture to change quite a bit once NVMe hits the scene. But for now, Windows 8 lets us put these AHCI-based drives on equal footing.
And Samsung's XP941 shows that it's not held back by STORAHCI. The drive outmaneuvers the other PCIe-based data points in write service times, so long as it's attached to ASRock's Ultra M.2 slot. Going through Intel's Z97 chipset, regardless of whether you're talking about SATA 6Gb/s or M.2, results in a similar outcome.