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Sorry for the newbie and probably off-topic question, but here goes...

I heard somewhere that (some types of?) Flash memory would start loosing data after a few years without power due to the way they work, and that heat would exacerbate the problem. As I understood it, data was stored by charging some elements (e.g. those representing logical 1st), but this charge would decline over time.

Anyway, my question is about what it takes to "refresh" such storage, for example a USB Flash drive - is it enough to just plug it into the computer now and then... or must I actually read the data... or must I rewrite the data (e.g. copying the data around on the flash drive, or copying it to the computer and back) ?

fluffy
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Baard Kopperud
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3 Answers3

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The post How to refresh the contents of a flash drive has an answer by a Kingston representative, which should apply to most flash devices:

Flash products built by Kingston are not built for archival purposes but if they are used in this capacity the best way to ensure the data integrity is maintained throughout the life-time of the product is to read all the data off the drive, perform a HDDErase cycle to clear all blocks and lastly, rewrite all the data back to the drive.

Unfortunately there is little information available from studies into this field to decisively state the exact frequency that this should be done since the error correction capability varies between the various NAND flash mediums and their featured controllers/software. There on-going discussions by IEEE and various standards groups to enhance and study this field further.

Hard disk drive manufacturer readily recommend performing a read and re-write on their hard disk drives every 3 years for archival purposes and I would suggest doing the same with NAND flash based products, even when the contents of the stated NAND flash based products are not modified by a read-erase-write cycle.

Plugging the device into the computer now and then won't help, ditto read the data.

You really must rewrite the data to refresh it.

harrymc
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The controller of the flash memory is in charge of periodically refreshing the data (the controller is also in charge of the wear-leveling, the garbage collection,...). This kind of information for a particular model is however difficult, if not impossible, to find. I am pretty sure that any decent SSD has some built-in data refresh capability (so it is enough to power it from time to time (the question is "how long", though...)), but I wouldn't bet for a 1$ USB key!

PierU
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Reading won't help, I can confirm that from personal experience for SD Cards used in a mobile music player over years. Over the time the player started to choke on certain files and it turned out the files read without reported error but are corrupted. There are differences if compared to copies stored on a hard drive. No error correction on those cheap cards it seems.

xenoson
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