Linux Symposium

I/O Subsystem Enhancements to Harness Solid State Storage

Suri Brahmaroutu

Enterprise Solid State Storage (SSS) are high performing class devices targeted at business critical applications that can benefit from fast-access storage. While it is exciting to see the improving affordability and applicability of the technology, enterprise software and Operating Systems (OS) have not undergone pertinent design modifications to reap the benefits offered by SSS.

This paper investigates the I/O submission path to identify the critical system components that significantly impact SSS performance. Specifically, our analysis focuses on the Linux I/O schedulers on the submission side of the I/O. We demonstrate that “one size fits all” scheduler policy doesn’t work well for SATA SSS. Of the current crop of schedulers, the Deadline scheduler offers up to 15% performance advantage over Noop and therefore it is best suited for most I/O intensive enterprise applications.

Further, we establish that all I/O schedulers including Deadline are not optimal for PCIe SSS, quantifying the possible performance improvements with a new design that leverages device level I/O ordering intelligence and other I/O stack enhancements. Finally, a new approach for PCIe SSS is presented that bypasses conventional Linux I/O request management and pushes requests out to the device with minimal processing in the software stack. The study quantifies performance gains of up to 200% in some specific I/O patterns and up to 50% in some real world workload scenarios for PCIe SSS.

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