Re: [PATCHES] O_DIRECT for WAL writes

On 6/23/05, Gavin Sherry <swm@linuxworld.com.au> wrote:

> > inertia) but seeking to a lot of new tracks to write randomly-positioned
> > dirty sectors would require significant energy that just ain't there
> > once the power drops.  I seem to recall reading that the seek actuators
> > eat the largest share of power in a running drive...
>
> I've seen discussion about disks behaving this way. There's no magic:
> they're battery backed.

Nah this isn't always the case, for example some of the IBM deskstars
had a few tracks at the start of the disk reserved.. if the power
failed the head retracted all the way and used the rotational energy
to power it long enough to write out the cache..  At start the drive
would read it back in and finish flushing it.

.... unfortunately firmware bugs made it not always wait until the
head returned to the start to begin writing...

I'm not sure what other drives do this (er, well do it correctly :) ).