linux-kernel - Re: Race to power off harming SATA SSDs

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Message-ID: <7ee84982-cfad-94d7-4e22-4edbeb852b32@redhat.com>
Date:   Mon, 8 May 2017 11:09:43 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Ricard Wanderlof <ricard.wanderlof@...s.com>,
        David Woodhouse <dwmw2@...radead.org>
Cc:     Pavel Machek <pavel@....cz>, Tejun Heo <tj@...nel.org>,
        boris.brezillon@...e-electrons.com, linux-scsi@...r.kernel.org,
        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

Hi,

On 08-05-17 11:06, Ricard Wanderlof wrote:
> 
> On Mon, 8 May 2017, David Woodhouse wrote:
> 
>>> On Mon, 8 May 2017, David Woodhouse wrote:
>>>> 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?
>>
>> Not that I'm aware of. Once we have reached the "it does happen and we
>> have to cope" there was not a lot of point in working out *why* it
>> happened.
>>
>> In fact, the only examples I *personally* remember were on NOR flash,
>> which takes longer to erase. So it's vaguely possible that it doesn't
>> happen on NAND. But really, it's not something we should be depending
>> on and the software mechanisms have to remain in place.
> 
> My point is really that say that the problem is in fact not that the erase
> is cut short due to the power fail, but that the software issues a second
> command before the first erase command has completed, for instance, or
> some other situation. Then we'd have a concrete situation which we can
> resolve (i.e., fix the bug), rather than assuming that it's the hardware's
> fault and implement various software workarounds.

You're forgetting that the SSD itself (this thread is about SSDs) also has
a major software component which is doing housekeeping all the time, so even
if the main CPU gets reset the SSD's controller may still happily be erasing
blocks.

Regards,

Hans