Re: Doubts on IO requests in USB subsystem

[Oliver Neukum]

On Mon, 2013-09-09 at 08:20 +0000, Morales, Alejandra wrote:
> mounted and there is no application using them at the moment, so that
> I was expecting that none
> of them receive file system requests. Indeed the SATA HD does not
> receive any requests unless I
> mount or unmount it, but the USB HD receives a large number of file
> system requests and it seems
> that it never enters into an idle state. Since any application is
> using it I think these requests may
> come from the USB subsystem. Am I right? If so, how could I determine
> whether a request comes
> from the USB subsystem or it is a file system request that actually
> moves blocks?

Your prime suspect is the detection of medium change which was
moved into the kernel in 3.2 or so. It can be disabled by sysfs.
Generally the notion that a certain task originates a read or write
on a block device is iffy. Read-ahead and shared data structures
make it impossible to accurately tell.

USB storage devices are notorious for setting the removable bit
even if they have no removable medium.

	Regards
		Oliver


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