[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <1494231215.6528.22.camel@infradead.org>
Date: Mon, 08 May 2017 09:13:35 +0100
From: David Woodhouse <dwmw2@...radead.org>
To: Ricard Wanderlof <ricard.wanderlof@...s.com>
Cc: Pavel Machek <pavel@....cz>, Tejun Heo <tj@...nel.org>,
boris.brezillon@...e-electrons.com, linux-scsi@...r.kernel.org,
Hans de Goede <hdegoede@...hat.com>,
linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
linux-mtd@...ts.infradead.org,
Henrique de Moraes Holschuh <hmh@....eng.br>
Subject: Re: Race to power off harming SATA SSDs
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 :)
Download attachment "smime.p7s" of type "application/x-pkcs7-signature" (4938 bytes)
Powered by blists - more mailing lists