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Disk I/O in Linux

Staelin, Carl


Keyword(s): disk performance; RAID; Linux; I/O performance

Abstract: The paper contains preliminary results from an investigation comparing Linux and WindowsXP disk I/O using kernel-based software RAID on identical hardware. WindowsXP performance is shown to be substantially superior to Linux performance, for reasons not currently understood. One known problem with the Linux RAID driver is that in Linux 2.4 file I/O is synchronous and file operations are serialized by a kernel file lock. Since the RAID driver is exposed to user-level applications via a file interface, this means that all accesses to the RAID are serialized. There are a number of possibilities to improve disk I/O performance: [1] Develop a user-level RAID layer built on aio and extend applications to allow asynchronous I/O. [2] Attempt to debug the Linux software RAID device so its synchronous performance is comparable to WindowsXP. We developed a simple user- level RAID layer built on aio, and demonstrate its improved performance over the Linux software RAID implementation, but its performance is still lower than that of the WindowsXP software RAID implementation. The alternative is to investigate various options for extending or improving the Linux kernel, which is likely to be a riskier and more difficult task.

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