Re: Race to power off harming SATA SSDs

[Ricard Wanderlof]

On Mon, 8 May 2017, David Woodhouse wrote:

> > I've got a problem with the underlying mechanism. How long does it take toÂ
> > erase a NAND block? A couple of milliseconds. That means that for an eraseÂ
> > to be "weak" du to a power fail, the host CPU must issue an erase command,Â
> > and then the power to the NAND must drop within those milliseconds.Â
> > However, in most systems there will be a power monitor which willÂ
> > essentially reset the CPU as soon as the power starts dropping. So inÂ
> > practice, by the time the voltage is too low to successfully supply theÂ
> > NAND chip, the CPU has already been reset, hence, no reset command willÂ
> > have been given by the time NAND runs out of steam.
> > 
> > Sure, with switchmode power supplies, we don't have those large capacitorsÂ
> > in the power supply which can keep the power going for a second or more,Â
> > but still, I would think that the power wouldn't die fast enough for thisÂ
> > to be an issue.
> > 
> Our empirical testing trumps your "can never happen" theory :)

I'm sure it does. But what is the explanation then? Has anyone analyzed 
what is going on using an oscilloscope to verify relationship between 
erase command and supply voltage drop?

/Ricard
-- 
Ricard Wolf WanderlÃf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30