[maemo-users] Limited life of flash memory

[From: Mark]

On Wed, Dec 3, 2008 at 2:01 AM, Frantisek Dufka <dufkaf at seznam.cz> wrote:
> Mark wrote:
>>
>> On Tue, Dec 2, 2008 at 9:36 AM, Igor Stoppa <igor.stoppa at nokia.com> wrote:
>>>
>>> I can only repeat my advice: why don't you do some reading at least
>>> about jffs2?
>>>
>>
>> Because it's irrelevant in discussions about removable flash memory.
>
> How do you know if you did not read it? :-) I wouldn't be surprised if jffs2
> technical documentation would discuss NAND pecularities and wear levelling
> details.
>

Because I have read it, and lots of other stuff.

> Also http://en.wikipedia.org/wiki/Wear_leveling and pdf whitepapers linked
> on the bottom could explain a lot.
>
>> Another issue is that wear levelling depends on there being a certain
>> amount of free memory in order to shuffle the data around. Most use
>> dynamic rather than static wear levelling, which reduces the
>> effectiveness even further when there is little free space.
>
> Flash translation layer in memory cards does not know about 'free space',
> that is filesystem related thing one layer above, we are talking about pure
> data blocks with no meaning here.
>
> That is actually one thing to improve in future, filesystem should let the
> flash device driver know which blocks are free so it can be more creative
> with them.
>
> Frantisek
>

...by which you're admitting that no wear levelling algorithm is perfect...

Let's go back to the original question: how reliable are flash memory
cards when used for booting an OS?

Answer: Probably "reliable enough", provided something else doesn't go
wrong. Flash cards *do* sometimes fail, for varying reasons, and
repeated writes aren't the only issue.

Mark