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
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