Fragmentation can impact embedded Flash systems

September 28, 2018

garyhilson-September 28, 2018

TORONTO — Gone are the days of having to manually defrag your hard drive because it's done automatically, and flash doesn't experience file fragmentation. Or does it?

It may be that your smartphone is running slow because it can't keep up with software updates and bloating, but that its flash storage is experiencing file fragmentation. Joel Catala, director of Embedded Solutions at Tuxera, said that contrary to popular belief, fragmentation can significantly affect performance of a flash device. Recent research suggests that as flash storage hardware gets faster, the software I/O stack overhead is an I/O performance bottleneck, he said in a telephone interview with EE Times. It's not the flash or the controller responsible for the bottleneck.

“Any flash vendor will tell you the controller is totally fine with it,” he said. But there's many more read calls to different areas of the flash drive that leads to fragmented data, said Catala. “That's where we have seen that performance gets a big drop.”

Much of the research on flash fragmentation is based on smartphone use cases. But Tuxera's position is that it becomes more than just an inconvenience as flash gets integrated into mission critical systems for automotive.

In a recent whitepaper, the company cites research that found an aged file system caused a performance slowdown on mobile flash hardware of two to five times. For most users, the degradation is rather fleeting, and the performance costs of aging are built into their expectations of file systems performance. Quite simply, we expect our smartphones to slow down, assuming it's because of the app and OS updates, and replace the device within two or three years.

Tuxera's testing as found that as flash storage reaches capacity, ext4 becomes very fragmented, performance dropps, and latency has very sharp spikes as compared to its own file system.

Because smart cars use similar flash storage technologies, Tuxera suspects these mobile storage issues also plague automotive storage, said Catala. Its solution is a proprietary file system instead of Ext4, which is not only one of the most commonly used file systems in mobile phones, but in the automotive industry as well. Ext4 is considered a good option for low-data or single-stream automotive use cases, and it's open-source. However, he said, when it comes to applications that handle a lot of data and multiple data streams, things get trickier, and over the long term the degree of fragmentation gets worse as more data is written to the storage, and performance consequently drops.

>> Continue reading this article on our sister site, EE Times: "Flash file fragmentation needs a fix for automotive."


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