The ECC needs to be stored. as ones ane zeroes

By: anon2 (, November 26, 2022 2:00 am
Room: Moderated Discussions
Heikki Kultala ( on November 25, 2022 11:48 pm wrote:
> anon2 ( on November 25, 2022 4:07 pm wrote:
> > Heikki Kultala ( on November 25, 2022 7:31 am wrote:
> > > The ECC needs to be stored. as ones ane zeroes
> >
> > ECC can be stored out of band. Flash controllers can disable on chip ECC and do their own.
> >
> > Then, depending on the translation layer, ECC adjustments could be written independently,
> > e.g., streamed out to the log. If you had a frequently updated page, you could keep the ECC
> > in a cache even, and only write it out on power failure or when the page is filled.
> >
> > I don't know of if anybody is actually doing that (multi programming the NAND) or if it would
> > be very useful or even possible. Programming a modern NAND is a fine art and there are all
> > sorts of effects from every operation (read, program, erase) including on nearby devices.
> Storing the ECC to totally separate place as the data is horribly inefficient.
> Two reads to totally separate places is considerably more expensive than one slightly wider read.

Yeah that is true.

> And storing the ECC bits to somewhere else does not solve the actual problem - they still have to
> be erased. If storing them to different kind of flash memory that has much smaller erase blocks -
> then that memory is MUCH more expensive per bit than the memory used to store the actual data.
> Making everything much bigger, more expensive, slower and more power-hungry.

No that's not the case, log structured devices can present a logical layer that is essentially random access, and if you have the right hardware (e.g., a small page fill buffer that can persist the last unwritten page of data if there is a power failure) then the program/erase side does not matter.

> That something is theoretically possible and that something makes sense are totally different things.

But you're still right about data requiring two reads being inefficient.
< Previous Post in Thread 
TopicPosted ByDate
Is 1 more expensive than 0?Andrey2022/11/21 05:23 AM
  Is 1 more expensive than 0?Juha Lainema2022/11/21 06:15 AM
  Is 1 more expensive than 0?Adrian2022/11/21 07:21 AM
    Is 1 more expensive than 0?anon22022/11/21 05:29 PM
  switching between 0 and 1 is what consumes powerHeikki Kultala2022/11/21 07:23 AM
    Thank you all for your answers. (NT)Andrey2022/11/21 08:29 AM
  Is 1 more expensive than 0?Foyle2022/11/21 08:58 AM
    Is 1 more expensive than 0?Michael S2022/11/21 10:51 AM
    Is 1 more expensive than 0?Captain Obvious2022/11/21 11:29 AM
      obvious stuffanonymou52022/11/21 02:25 PM
        obvious stuffAndrey2022/11/21 02:50 PM
          obvious stuffMichael S2022/11/21 03:43 PM
  SRAM is bistableAnon2022/11/21 10:50 AM
    SRAM is bistableAndrew Clough2022/11/22 05:53 AM
  NAND Flash 1 and 0jokerman2022/11/24 01:13 PM
    NAND Flash 1 and 0Joern Engel2022/11/25 12:00 AM
      NAND Flash 1 and 0Ungo2022/11/25 02:26 AM
        The ECC needs to be stored. as ones ane zeroes (NT)Heikki Kultala2022/11/25 08:31 AM
          The ECC needs to be stored. as ones ane zeroesanon22022/11/25 05:07 PM
            The ECC needs to be stored. as ones ane zeroesHeikki Kultala2022/11/26 12:48 AM
              The ECC needs to be stored. as ones ane zeroesanon22022/11/26 02:00 AM
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