On Tue, 2008-12-02 at 09:10 -0700, ext Mark wrote: > On Tue, Dec 2, 2008 at 12:43 AM, kenneth marken <kemarken@xxxxxxxxxxxx> wrote: > > On Tuesday 02 December 2008 00:52:47 Mark wrote: > >> Unfortunately, this makes some fundamental assumptions that aren't > >> correct, such as that "the whole card" is involved when writing and > >> that it's sequential. Actually, some areas of the card are going to > >> get very heavy use and others very little, especially if an OS is > >> installed on it. Even without an OS, some files are going to be > >> written much more often than others. All it takes is for one critical > >> area (not the whole card) to burn out in order for you to lose data, > >> possibly even catastrophically. The bottom line is that 580 years > >> would be *extremely* optimistic. That said, it's fairly safe to say > >> that you'll either switch to a new device or get a larger and/or > >> faster card long before the current one wears out. > >> > > > > ever heard of wear leveling? just about any product has it these days. > > > > this means that while the filesystem things the files are in the exact same > > place as last time, the actual area of the chip being used is different, so > > even with specific files being hit hard (i know i have heard a horror storry > > about someone burning out the first sector of a no-name usb stick thanks to > > having the mounting set to updating the FAT for each change done, but that was > > some years ago when flash drives where a novelty), the wear should be spread > > out over the whole chip. > > > > "Should be" and "are" are two different things, and there are still > some problems with your assertions. In order for files to be in > different places, they have to be moved, which means at least another > write operation. In practice, there's a limited amount of that kind of > thing that can be done without both slowing everything down to the > point of uselessness and creating the very problem you're trying to > prevent. > > ...Which is all irrelevant if there happens to be a sector that is > defective from the factory. Sometimes a defect doesn't show up in > quality-control tests but does after the consumer buys and uses the > product. > > > on internal chips, like on the 770 or the N8x0's, one can use a wear leveling > > FS. but that would mean that your writing directly to flash without some kind > > of controller chip sitting inbetween. > > > > also, flash being flash, the error will shop up on write, not on read. and > > will not stop the drives readability. so being able to siphon out what data is > > in there can still be possible (iirc). > > > > That's not entirely correct. If the bits that fail happen to be where > the inodes or other critical filesystem data are stored, you're > screwed. Also, errors on read do in fact happen. I've had major > name-brand flash cards fail, and in fact I've had better luck with the > no-name cards than the name brands thus far, both with speed and > reliability. I would recommend you to do some reading about jffs2, ubifs and wear levelling in general. Then you'll understand better what people are trying to tell you. -- Cheers, Igor --- Igor Stoppa Maemo Software - Nokia Devices R&D - Helsinki _______________________________________________ maemo-users mailing list maemo-users@xxxxxxxxx https://lists.maemo.org/mailman/listinfo/maemo-users
