[Coco] CF and SD life expectancy

[Roger Taylor]

At 04:31 PM 7/24/2011, you wrote:
>Interesting. Cross posted from the BBC-Micro mailing list.
>
>QUOTE:
>Most of the consumer-grade CF and SD cards you can buy today are 
>probably using MLC flash which requires fairly careful supervision 
>if you want your data to stay intact.  In particular, each block of 
>MLC can only be read from a certain number of times before it needs 
>to be erased and rewritten. There's also the wear-levelling issue 
>which is more severe with MLC because the write cycle endurance of 
>each block is less than SLC by about a factor of 10.
>
>That's not to say that it's necessarily impossible to make a 
>reliable card out of MLC, but it requires a fairly sophisticated 
>controller and my experience has been that a lot of the lower-end 
>cards either don't have the right level of technology for that, or 
>haven't been appropriately tested and don't actually work 
>correctly.  On some of the cards we tested recently at work, just 
>reading from the same file a couple of thousand times would cause 
>the data to gradually become corrupt.
>/QUOTE
>
>Remember that NitrOS9 reads the first sector and the File Allocation 
>sectors *frequently*.
>
>Regards, Bob Devries
>Dalby, QLD, Australia
>
>--
>Coco mailing list
>Coco at maltedmedia.com
>http://five.pairlist.net/mailman/listinfo/coco


We've dealt with flakey floppy disks since 1980 and now memory cards 
are far more reliable, yet we worry more.  So once every 3 years or 
so you can run a sector refresher over the entire card or just clone 
the card onto a new one.  They're cheaper than a bag of potato chips.

Why not just test your theory with a looping BASIC program that reads 
LSN0 forever until you get corrupt sector data, and post what the 
read count was.  Do the same with a write/read test to LSN0 on 
another card and post your results.  With a program running around 
the clock, it shouldn't take long to solve this mystery.  Also take 
note of the date/time so we can estimate the lifespan we can expect 
from typical usage on the CoCo.





-- 
~ Roger Taylor