Tracking down a workqueue io source

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I worked up some patches to use the ata SLEEP command instead of STANDBY to save more power, but I have found that something in the kernel keeps issuing a request to the disk ( no mounted filesystems on it ) every 10 minutes. This request resets the link bringing the disk back up to STANDBY mode. blktrace shows the process name is "pool" so I guess it is a work queue item? Inserting a dump_stack() was not helpful. How can I track down the source of this request?

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