Eric,
> On 5/16/05, Robert Hancock <[email protected]> wrote:
> > If the power to the drive is truly just cut, then this is basically
> > what will happen. However, I have heard, for what it's
> worth, that in
> > many cases if you pull the AC power from a typical PC, the
> Power Good
> > signal from the PSU will be de-asserted, which triggers the
> Reset line
> > on all the buses, which triggers the ATA reset line, which triggers
> > the drive to finish writing out the sector it is doing. There is
> > likely enough capacitance in the power supply to do that
> before the voltage drops off.
>
> Yes, but as you said this isn't a power loss event. It is a
> hard reset with a full write cache, which all drives on the
> market today respond to by flushing the cache.
>
> According to the spec the time to flush can exceed 30s, so
> your PSU better have some honkin caps on it to ensure data
> integrity when you yank the power cord out of the wall.
why don't drive vendors create firmware which reserved a cache-sized
(e.g. 2MB) hole of internal drive space somewhere for such an event, and
a "cache flush caused by hard-reset" simply caused it to write the cache
to a fixed (contiguous) area of disk.
the same drive firmware on power-on could check that area and 'write
back' the data to the correct locations.
all said and done, why wouldn't a vendor (lets just say "Maxtor" :) )
implement something like this and market it as a feature?
i'd happily spend a few extra bucks for something that given a modern
PSU providing a few Hz of power (e.g. 50msec) provided higher data
reliability in case of power failure..
cheers,
lincoln.
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