--- In Alan Dayley <> wrote:
>
> On Sun, Feb 8, 2009 at 12:33 PM, marek.zukal <> wrote:
> > Hi,
> >
> > I would like to know, if there is a way how to learn a wear level of
> > an SD card. Are there any tools or is it somehow possible to get some
> > info about number of cycles the blocks on the card have been through
> > and how many cycles they are set to withstand? I find it very
> > disturbing that the only information about SD card life time is very
> > unspecific number of 100 000 to million cycles for a block. It would
> > be great to have some way to determine how stressed are different
> > parts of the file system when used in action and how many writes are
> > performed on individual blocks. I will appreciate any advice or
> > experience. Thanks in advance.
>
> Marek,
>
> The wear leveling of the flash's physical blocks is performed by the
> flash controller in the SD Card. The flash controller not only
> provides the SD interface to the host and the data transfer but has
> all the code for wear leveling, sparing and other "housekeeping"
> duties required for the flash to work well.
>
> Flash controller manufacturers do NOT reveal details about all of this
> without an NDA in place, and then only if you pry it out of them. If
> they do give you information and tools, a great deal of this sort of
> information can be extracted. There are a number of flash controller
> manufacturers with many of the SD card makers simply purchasing
> controllers and knowing very little about their internals. You have
> to have a tight relationship directly with the controller
> manufacturer, forged over time and business, to gain such information.
>
> Your best, quick answer is to characterize how your application writes
> to the card. How many writes, for what length, over how much time,
> etc. and use these answers to estimate when you will be close to the
> SD card manufacturers stated write endurance. The set up a
> replacement schedule to pull old cards out before they get to the
> failure. Not an easy answer but getting the access to the data you
> describe is actually harder, unless you have a huge population and
> business reasons to establish such relationships with the controller
> maker.
>
> The above is based on my 8+ years experience working with flash
> controllers. It is a secret world that the makers don't open to just
> anyone.
>
> Alan
>
Thank you very much for this answer. I actually thought that it would
be that way but I had to try it.
The thing is that I need no huge space for data. Just a few MB but
definitely more than any battery backed ram module from TS provides,
so the flash is the best way. I am most worried about the superblock
of the file system because this is where the most of the stress will
be since the files are just small logs. And I have not seen any
description of any card that would say "The wear balancing on this
card is done by physical block rotation, remapping etc." so it would
benefit from the fact that most of the card is actually unused. I
found a lot of papers about flash wear balancing but everything was
very general. I know that these cards are consumer electronics in the
first place but I would expect the manufacturers to be more embedded
friendly.
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