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Re: Race to power off harming SATA SSDs

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On Mon, 2017-05-08 at 09:38 +0200, Ricard Wanderlof wrote:
> On Mon, 8 May 2017, David Woodhouse wrote:
> 
> > 
> > > 
> > > [Issue is, if you powerdown during erase, you get "weakly erased"
> > > page, which will contain expected 0xff's, but you'll get bitflips
> > > there quickly. Similar issue exists for writes. It is solveable in
> > > software, just hard and slow... and we don't do it.]
> > It's not that hard. We certainly do it in JFFS2. I was fairly sure that
> > it was also part of the design considerations for UBI ? it really ought
> > to be right there too. I'm less sure about UBIFS but I would have
> > expected it to be OK.
> I've got a problem with the underlying mechanism. How long does it take to 
> erase a NAND block? A couple of milliseconds. That means that for an erase 
> to be "weak" du to a power fail, the host CPU must issue an erase command, 
> and then the power to the NAND must drop within those milliseconds. 
> However, in most systems there will be a power monitor which will 
> essentially reset the CPU as soon as the power starts dropping. So in 
> practice, by the time the voltage is too low to successfully supply the 
> NAND chip, the CPU has already been reset, hence, no reset command will 
> have been given by the time NAND runs out of steam.
> 
> Sure, with switchmode power supplies, we don't have those large capacitors 
> in the power supply which can keep the power going for a second or more, 
> but still, I would think that the power wouldn't die fast enough for this 
> to be an issue.
> 
> But I could very well be wrong and I haven't had experience with that many 
> NAND flash systems. But then please tell me where the above reasoning is 
> flawed.

Our empirical testing trumps your "can never happen" theory :)

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Re: Race to power off harming SATA SSDs Pavel Machek <pavel@ucw.cz> - 2017-05-08 00:00 +0200
  Re: Race to power off harming SATA SSDs David Woodhouse <dwmw2@infradead.org> - 2017-05-08 09:30 +0200
    Re: Race to power off harming SATA SSDs Ricard Wanderlof <ricard.wanderlof@axis.com> - 2017-05-08 09:40 +0200
      Re: Race to power off harming SATA SSDs David Woodhouse <dwmw2@infradead.org> - 2017-05-08 10:20 +0200
        Re: Race to power off harming SATA SSDs Ricard Wanderlof <ricard.wanderlof@axis.com> - 2017-05-08 10:40 +0200
          Re: Race to power off harming SATA SSDs David Woodhouse <dwmw2@infradead.org> - 2017-05-08 11:00 +0200
            Re: Race to power off harming SATA SSDs Ricard Wanderlof <ricard.wanderlof@axis.com> - 2017-05-08 11:10 +0200
              Re: Race to power off harming SATA SSDs Hans de Goede <hdegoede@redhat.com> - 2017-05-08 11:10 +0200
                Re: Race to power off harming SATA SSDs David Woodhouse <dwmw2@infradead.org> - 2017-05-08 12:20 +0200
                Re: Race to power off harming SATA SSDs Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-05-08 14:00 +0200
                Re: Race to power off harming SATA SSDs David Woodhouse <dwmw2@infradead.org> - 2017-05-08 17:50 +0200
                Re: Race to power off harming SATA SSDs Pavel Machek <pavel@ucw.cz> - 2017-05-08 23:40 +0200
                Re: Race to power off harming SATA SSDs Pavel Machek <pavel@ucw.cz> - 2017-05-08 18:50 +0200
                Re: Race to power off harming SATA SSDs Tejun Heo <tj@kernel.org> - 2017-05-08 19:50 +0200
                Re: Race to power off harming SATA SSDs Pavel Machek <pavel@ucw.cz> - 2017-05-08 21:00 +0200
                Re: Race to power off harming SATA SSDs Tejun Heo <tj@kernel.org> - 2017-05-08 21:10 +0200
                RE: Race to power off harming SATA SSDs Atlant Schmidt <aschmidt@dekaresearch.com> - 2017-05-08 20:50 +0200
              Re: Race to power off harming SATA SSDs David Woodhouse <dwmw2@infradead.org> - 2017-05-08 12:20 +0200
    Re: Race to power off harming SATA SSDs Pavel Machek <pavel@ucw.cz> - 2017-05-08 11:30 +0200
      Re: Race to power off harming SATA SSDs David Woodhouse <dwmw2@infradead.org> - 2017-05-08 11:40 +0200
        Re: Race to power off harming SATA SSDs Pavel Machek <pavel@ucw.cz> - 2017-05-08 13:00 +0200
          Re: Race to power off harming SATA SSDs Richard Weinberger <richard.weinberger@gmail.com> - 2017-05-08 13:10 +0200
            Re: Race to power off harming SATA SSDs Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-05-08 14:00 +0200
            Re: Race to power off harming SATA SSDs Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-05-08 14:00 +0200
              Re: Race to power off harming SATA SSDs Richard Weinberger <richard@nod.at> - 2017-05-08 14:20 +0200
          Re: Race to power off harming SATA SSDs David Woodhouse <dwmw2@infradead.org> - 2017-05-08 13:20 +0200
            Re: Race to power off harming SATA SSDs Pavel Machek <pavel@ucw.cz> - 2017-05-08 14:40 +0200
      Re: Race to power off harming SATA SSDs Richard Weinberger <richard.weinberger@gmail.com> - 2017-05-08 12:00 +0200

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