Benchmarking Issues And Trends
We had a phone conference with Samsung engineers after finalizing our first benchmark runs on the 470-series. Performance numbers were encouraging, if not mind-blowing. We had a healthy discussion about benchmarking tools, as Samsung pointed out a possibly-critical limitation with c’t magazine’s h2benchw 3.6 tool. This is by far one of the best apps for accurately testing throughput across the full storage area of any drive, regardless of partitions. It returns a CSV file that allows users to draw data transfer diagrams. These show the average and minimum transfer rate results imperative in identifying throughput-oriented spikes and drops. Many SSDs are impressively fast, but we believe it’s almost as impressive to look at how slow they could be in a worst-case scenario.
h2benchw can cause issues because it doesn’t generate random data for writing. Instead, it writes only zeroes. This has not been an issue with hard drives nor with most SSDs, which treat all writes equally. However, SandForce’s “DuraClass” architecture works without a dedicated cache memory and utilizes some of the main flash memory for caching, load balancing, and countering write amplification. Since the algorithms are potentially smart enough to turn cache data into user data or to take advantage of data compression, this may represent a benefit for SandForce-powered SSDs.
For this reason, we followed Samsung’s recommendation and ran most of the SSDs on CrystalDiskMark 3.0, as well. It isn’t comprehensive enough to look at a drive’s overall throughput performance, but it’s very handy for assessing the performance potential of SSD products.
PCIe SSDs Coming Up
Finally, the issue of bandwidth limitations might come to an end in the foreseeable future. The SSD Form Factor Working Group was recently founded by Dell, EMC, Fujitsu, IBM, and Intel in an effort to simplify SSD installation and maintenance. Other companies such as Amphenol, Emulex, Fusion-io, IDT, Marcel, Micron, Molex, PLX, STEC, SandForce, and Smart Modular Technology are Contributor Members. Collectivley, the group will primarily be working on interfaces and form factors. One predictable result will be a connector and interface specification that will support storage over PCI Express 3.0 and include better interoperability with SAS/SATA 3.0. Improved hot plugging is another priority.
Future SSDs will most likely be limited to a 6.35 mm z-height. A slimmer design will enable significantly higher storage and I/O densities in high-performance environments. Today’s SSDs are typically housed in 7 mm or 9.5 mm housings on the 2.5” form factor.