Re: dummy file read periodically for external USB Hard Disk

[Dave Jones <davej@redhat.com>]

On Tue, Jul 08, 2014 at 01:01:27PM +1000, NeilBrown wrote:
 > On Mon, 7 Jul 2014 22:42:29 +0800 loody <miloody@gmail.com> wrote:
 > 
 > > hi all:
 > >     we met a USB Hard Disk that will go to suspend if host stop
 > > sending scsi read command over 5mins.
 > >     To save the IO, kernel will keep the file in page cache as much as
 > > he can and under this circumstances, the read command may disappear
 > > for a while longer enough to cause the device suspend.
 > > 
 > >     is there any kernel config or module parameter can do the dummy
 > > read periodically, even the sector 0 (MBR) is fine.
 > >     or is there any kernel api I can use to read sector 0(MBR) maybe
 > > every 4mins?
 > 
 > Open the device with O_DIRECT and read a block every 4 minutes.
 > That should keep it awake.

modifying /sys/module/usbcore/parameters/autosuspend might also have the
desired effect without the need for periodic reads.

	Dave