On Mon, 9 Feb 2009, Alan Dayley wrote:
> On Mon, Feb 9, 2009 at 10:14 AM, Jim Jackson <> wrote:
>>
>> That's good. Re-using just a small percentage of a large flash card, allows
>> the wear leveling to cycle thru' a higher percentage of free blocks, and so
>> means the flash lasts longer.
>>
>> One of the worse situations is to have a card 95% full with static data,
>> and you are rewriting data in the remaining 5%. The wear levelling can only
>> cycle round the small percentage of free blocks, so they wear out quicker.
>
> The wear-leveling behavior you described here is known as "dynamic
> wear-leveling." This means the empty or unused flash blocks and the
> blocks that are dynamic, or changing, in the current transaction are
> the only ones involved with the wear-leveling by the controller. Some
> controllers also include any spare reserve blocks in the dynamic
> wear-leveling.
>
> As of a few years ago, a better algorithm has been deployed by most
> flash controller makers. This is known as "static wear-leveling" and
> includes ALL flash blocks, including those with static data. In
> static wear-leveling the writes are moved all around the flash media,
> even moving around previously written blocks of user data. This
> obviously improves the spread out of the wear on the flash.
Thanks for this, I'd not come across static wear-leveling, but google
provides :-)
It does of course imply added time for writes where there is lots of static
data.
>
> Which does your controller use? Well, that's hard to know for all the
> reasons we have already discussed in this thread. However, over the
> past two years or so all controllers have been moving to the static
> wear-leveling model to get maximum life out of the flash. If you
> bought your SD cards within the last two years or so, you should be
> enjoying the better algorithm. Also, if your memory card is billed as
> "industrial" or "extended wear" or something like that, it almost
> positively has the better algorithm or static wear-leveling in use.
>
> Alan
>
------------------------------------
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/ts-7000/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/ts-7000/join
(Yahoo! ID required)
<*> To change settings via email:
<*> To unsubscribe from this group, send an email to:
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
|