On Wednesday 03 December 2008 12:26:29 Mark wrote: > On Wed, Dec 3, 2008 at 2:01 AM, Frantisek Dufka <dufkaf@xxxxxxxxx> wrote: > > Mark wrote: > >> On Tue, Dec 2, 2008 at 9:36 AM, Igor Stoppa <igor.stoppa@xxxxxxxxx> 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 _______________________________________________ maemo-users mailing list maemo-users@xxxxxxxxx https://lists.maemo.org/mailman/listinfo/maemo-users
