Retention Time for Flash Memory

I am considering using flash memory, in the form of SD cards, as a means of complementing my regular DVD backups. The cards are getting reasonably cheap and have an impressive data density. However, I have read that such memory has only a limited retention time.

Hence, I am wondering:

• Firstly, considering that such memory has been around for a while, is any empirical data available regarding retention times? The best I've been able to come up with is using the manufacturers warranty as a baseline.
• Secondly, does rewriting the memory periodically `reset' the clock, so to speak?

Solution 1:

One of the problems with empirical data is that the kind of memory that has been around long enough to get natural empirical data is so old that it isn't manufactured anymore. What they do instead is heat it up, which greatly increases the speed at which the data is lost, and based on how long it retains data when heated the can estimate how long it will retain data in normal circumstances.

As they've been moving to smaller process geometries the data retention time has shortened. 3xnm MLC is usually rated for 5+ years of data retentions. The new 2xnm stuff they are coming out with now is supposed to be a bit shorter. 4 years I would guess. Lower temperatures will lengthen this time.

Yes, if you rewrite it it will get refreshed.