On Tue, 28 Nov 2000, Tom Lane wrote:
> Nathan Myers <ncm@zembu.com> writes:
> > In the event of a power outage, the drive will stop writing in
> > mid-sector.
>
> Really? Any competent drive firmware designer would've made sure that
> can't happen. The drive has to detect power loss well before it
> actually loses control of its actuators, because it's got to move the
> heads to the safe landing zone. If it checks for power loss and
> starts that shutdown process between sector writes, never in the
> middle of one, voila: atomic writes.
In principle, that is correct. However, the SGI XFS people
have apparently found otherwise -- what can happen is that
the drive itself has enough power to complete a write, but
that the disk/controller buffers lose power and so you end
up writing a (perhaps partial) block of zeroes.
Matthew.