[Nottingham] USB flashing your distro?

[Camilo Mesias]

Hi,

> But are you sure it was due to them running out of write cycles?
>  Hard disks fail too.

According to the fault analysis from the manufacturers, some did.
There are many other faults though - ranging from the firmware bugs
corrupting internal tables to electrical damage to the flash chip. As
you said, hard disks can fail too (and in several ways).

Sometimes the CF firmware detects flash failures and swaps out bad
sectors. When it has no more spare sectors it can go into a 'read
only' mode. Heavy writing will increase the chances of this happening.

Also writing can apparently affect adjacent cells in the flash chip
under some circumstances, so old data might get corrupted when new
data is written nearby. Another reason to write less if possible.

> True, but with the very low cost of these products I am not
>  surprised they aren't willing to state anything complicated like
>  that.  Crucial offer a lifetime warranty.  Kingston offer a lifetime
>  warranty.  SanDisk offer a 5 year warranty.
>
>  Kingston CF media is rated for 10,000 write cycles per sector with
>  wear levelling - they state that this will last for 27 years of
>  rewriting the entire media once per day.

All those warranties are based on statistical models which assume less
writing than is possible with an embedded system, and they will
replace the media rather than cover your costs incurred. If you have a
journalling FS and lots of little writes (eg. appending to log files)
then it can be very harsh on the underlying flash chips.

I've worked on a product that uses these CF cards and have come to the
conclusion that they are a necessary evil. They are loads better than
little hard drives and ridiculously cheap, but they don't last forever
and it's essential to minimise writes and have a 'plan B' for when
they fail.

-Cam