[maemo-users] Limited life of flash memory

[From: Brian Waite]

On Wednesday 03 December 2008 12:26:29 Mark wrote:
> 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...
I agree with that. Also no spinning media is perfect either
From my experience, (only about 10 yrs, not an eternity) flash drives have a 
higher life expectency than any spinning media I have used. I have had far 
more hard drives die than FLASH devices.  I have seen numbers to argue FLASH 
life expectancy to be an order of magnitude better than spinning media. 

I am not taking into account dropping my thumbdrive every other day and 
slamming books on SD cards. 

If I were to put a Flash drive beside a hard drive and do that same activity 
to them (say a typical user type load of reads/writes). I expect that the hard 
drive would die statistically more often. 
>
> 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.

I would answer: More reliable than your PC harddrive. We trust our OSes on 
those why not on FLASH.

Thanks
Brian