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Solid-state storage devices and the block layer

Oct 15, 2010, 06:04 (1 Talkback[s])
(Other stories by Jon)

"Over the last few years, it has become clear that one of the most pressing scalability problems faced by Linux is being driven by solid-state storage devices (SSDs). The rapid increase in performance offered by these devices cannot help but reveal any bottlenecks in the Linux filesystem and block layers. What has been less clear, at times, is what we are going to do about this problem. In his LinuxCon Japan talk, block maintainer Jens Axboe described some of the work that has been done to improve block layer scalability and offered a view of where things might go in the future.

"While workloads will vary, Jens says, most I/O patterns are dominated by random I/O and relatively small requests. Thus, getting the best results requires being able to perform a large number of I/O operations per second (IOPS). With a high-end rotating drive (running at 15,000 RPM), the maximum rate possible is about 500 IOPS. Most real-world drives, of course, will have significantly slower performance and lower I/O rates.

"SSDs, by eliminating seeks and rotational delays, change everything; we have gone from hundreds of IOPS to hundreds of thousands of IOPS in a very short period of time. A number of people have said that the massive increase in IOPS means that the block layer will have to become more like the networking layer, where every bit of per-packet overhead has been squeezed out over time. But, as Jens points out, time is not in great abundance."

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