On Monday 01 December 2003 06:36 pm, Alan Cox wrote:
On Mon, Dec 01, 2003 at 09:33:17AM +0100, David Balazic wrote:
> So my question is , how can one test if the journalled FS on his disk is
> actually working
> as it should or is it just waste of time and giving a false sense of
> safety
Its extremely hard to do because you need fairly complex tools to
ensure
outstanding I/O during a sudden power off and out of order drive writeback
etc
What you need is a way of reading the AC mains coming into the power supply,
or readings of the DC rails. If the rail drops below a threshold value, it's
time to button up. With typical power supply output capacitors and/or low
loading on the rails, you might have up to half a second to react. One
wishes that the power supply could send a 'I'm about to croak!' signal to the
motherboard that the kernel could key off of, and it would be even nicer if
the PS had a flywheel capacitor set on all outputs before crowbarring (the
voltages have to be sequenced during powerfail as well as powerup).
I remember the intelligence behind the old Seagate ST251 stepper motor
actuator MFM hard drive. It auto parked at poweroff, by using the spindle
motor as a generator, driving the stepper to park. With servos that's not a
problem due to the spring tension that is a normal part of the voice coil
mechanism. That couldn't be done with a stepper.
So it can be done if there is hardware support. If the MB allows monitoring
of the DC rails, one could do such, no?
--
Lamar Owen
Director of Information Technology
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC 28772
(828)862-5554
www.pari.edu