APM doesn't spin the disk down in general. APM just set the disks own
spindown configuration at boot.
> 2 Whenever the disk is spun down sys_bdflush should be a noop
> The idea being that eventually a read will wake up the disk and all
> those dirty buffers will be flushed within five seconds. This will
> suck up a lot buffers but if the free list is empty refill_freelist
> will still work fine.
And if your machine crashes in that state you might lose hours of work.
Alan