[maemo-users] Limited life of flash memory

From: Mark wolfmane at gmail.com
Date: Tue Dec 2 01:52:47 EET 2008
On Mon, Dec 1, 2008 at 4:01 PM, kenneth marken <kemarken at broadpark.no> wrote:
> On Monday 01 December 2008 23:35:24 Sirio Negri wrote:
>> Hi all! I found some days ago a few articles about the limited life of
>> flash memory, specially for usb pendrive. The problem seems to be the
>> limited times you can write on it. Does it exist also for rs-mmc?
>> I know that the limit is very high (around 10 million of times) and it's
>> not a big problem for a normal user. But if you install an OS on it,
>> like on my Nokia 770, I think that the use of the memory card is bigger
>> and, if there is that problem, its life is shorter.
>> Thanks all for any info on it.
>> Sirio Negri
> iirc, the math goes something like this:
> take the space of the card, divide by write speed, thats how long it will take
> (in seconds) to do a write of the whole card.
> a 4GB card at 2MB pr second will take about half an hour to do a full write...
> now, if the card has a write limit of 10 million, that means it will take
> about 5 million hours...
> thats about 580 years of continual writing...
> yes, there are some cheap chips out there with poor wear leveling (meaning
> that one can burn out a single sector by repeatedly writing to it), but i
> suspect no name brand card will be that poorly made.

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.


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