Re: [PATCHES] O_DIRECT for WAL writes

[ on the other point... ]

Curt Sampson <cjs@cynic.net> writes:
> But is it really a problem? I somewhere got the impression that some
> drives, on power failure, will be able to keep going for long enough to
> write out the cache and park the heads anyway. If so, the drive is still
> guaranteeing the write.

If the drives worked that way, we'd not be seeing any problem, but we do
see problems.  Without having a whole lot of data to back it up, I would
think that keeping the platter spinning is no problem (sheer rotational
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...
        regards, tom lane