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Re: Shutdown behavior and flash storage devices

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On 7/24/2021 8:19 AM, Dave Nadler wrote:
> Hi All - I'm wondering what other folks do about this issue...
> 
> Consumer flash storage devices (USB memory stick, SD card, etc)
> have a nice internal wear-leveling controller. When one does a write operation, 
> lots of sectors may be internally rejiggered to provide uniform wear (so things 
> that are never rewritten from the application point of view are actually moved 
> around and rewritten). This activity is invisible from normal application's 
> point of view, but takes some time. If the device is powered off during such 
> activity, data corruption... So, its necessary to provide the device some time 
> after the last write before it is powered off. Plenty of embedded stuff I've 
> seen too often corrupts memory at power off, and of course the device 
> manufacturers blame the memory manufacturers...
> 
> So, how do you avoid this kind of corruption in your designs?

Two (transient) copies of each "chunk" of data.  Update the second
copy (on or before impending power fail).  When complete, toggle
a pointer to reference it as the most recent (assuming you don't
have metadata that automatically provides that sort of information).

The "first" copy can now be removed and its space reallocated to
some other "second copy"

Then, move on to the next "chunk".  Design your algorithms so that
you can tolerate some chunks being "stale" (not updated in time)
wrt the others.

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Shutdown behavior and flash storage devices Dave Nadler <drn@nadler.com> - 2021-07-24 11:19 -0400
  Re: Shutdown behavior and flash storage devices Theo <theom+news@chiark.greenend.org.uk> - 2021-07-24 16:37 +0100
  Re: Shutdown behavior and flash storage devices Don Y <blockedofcourse@foo.invalid> - 2021-07-24 18:10 -0700
    Re: Shutdown behavior and flash storage devices Dimiter_Popoff <dp@tgi-sci.com> - 2021-07-25 14:18 +0300
      Re: Shutdown behavior and flash storage devices Don Y <blockedofcourse@foo.invalid> - 2021-07-25 09:20 -0700
    Re: Shutdown behavior and flash storage devices Dave Nadler <drn@nadler.com> - 2021-07-25 08:49 -0400
      Re: Shutdown behavior and flash storage devices Don Y <blockedofcourse@foo.invalid> - 2021-07-25 09:30 -0700
      Re: Shutdown behavior and flash storage devices Dimiter_Popoff <dp@tgi-sci.com> - 2021-07-25 22:51 +0300
        Re: Shutdown behavior and flash storage devices Don Y <blockedofcourse@foo.invalid> - 2021-07-25 13:27 -0700
          Re: Shutdown behavior and flash storage devices Dimiter_Popoff <dp@tgi-sci.com> - 2021-07-26 00:00 +0300
            Re: Shutdown behavior and flash storage devices Don Y <blockedofcourse@foo.invalid> - 2021-07-25 17:35 -0700
  Re: Shutdown behavior and flash storage devices kegs@provalid.com (Kent Dickey) - 2021-07-25 13:53 -0500
    Re: Shutdown behavior and flash storage devices Don Y <blockedofcourse@foo.invalid> - 2021-07-25 13:20 -0700
  Re: Shutdown behavior and flash storage devices Jaded Hobo <badboy@heaven.org> - 2021-07-27 19:44 +0200
    Re: Shutdown behavior and flash storage devices Don Y <blockedofcourse@foo.invalid> - 2021-07-27 11:27 -0700

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