Nandflash lifetime calculation

[Jaap de Jong]

Hi Richard

thanks for the reply!

Sure, there are many other circumstances that influences the lifespan,

but my main interest here was the number of program/erase cycles.

Jaap



On 16-09-16 16:20, Richard Weinberger wrote:
> Jaap,
>
> On Fri, Sep 16, 2016 at 1:34 PM, Jaap de Jong <jaap.dejong at nedap.com> wrote:
>> Hi All!
>>
>> I'm wondering if my expected nandflash lifetime calculation is, well at
>> least, a bit accurate.
>>
>> So I have this nandflash and about half of it is occupied by static files.
>> It will not change.
>> The other half will be used by logs and databases, the dynamic part of this
>> UBI filesystem.
>> Their length will not change because they sort of act as circular buffers.
>> Let's say this system ran a year and the maximum erase counter is now at
>> 1.000.
>> The nandflash is specified at 100.000 cycles and is 512MB in size.
>> I added a factor of 0.7 for overhead.
>>
>> So I have a few assumptions, please correct me when and where I'm wrong:
>>
>>      1 - total space available for writing such a nandflash = 0.7 * 100.000 *
>> 512MB before it reaches
>>          its maximum if wear levelling is across the full device (global,
>> which UBI claims)
>>          --> 35840 GB
>>
>>      2 - when the maximum erase counter is at 1.000 in 1 year and 256MB is
>> being used for that,
>>          a total of about 1.000 * 256MB is written in 1 year
>>          --> 256 GB
>>
>>      3 - the expected lifetime of this nandflash with this usage then would
>> be 35840 / 256
>>          --> 140 yr
>>
>> Would that make any sense? (Except that it is far too long to even get close
>> to that....)
> Well, your calculation considers only one factor, the maximum number of P/E
> cycles.
> Please also keep read disturb and data retention in mind.
> And the environment also matters, mostly temperature.
>