# Micro SDHC cards



## balanga (Apr 30, 2017)

I have a number of Micro  SDHC cards which no longer work. I don't know what happened to them, do they suddenly just fail or do they simply deteriorate with use/time and is there a way to check their state whilst they are usable. I hate the idea of suddenly losing the data on a 64GB card, would prefer to know that it is becoming unreliable.


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## sko (May 3, 2017)

Just as any other flash drive (USB, CF, MMC, SD etc pp) they just die. I have had several pendrives and flash cards that just stopped working after a few years and most of them suffered from bitrot shortly before - the really cheap ones died earlier, the "better" ones (which still use cheap-but-not-THAT-bad NAND) lasted a bit longer.
These flash drives also suffer from bitrot if not powered over longer periods of time (a few months). They were never ment for backup purposes - never use them as such but back up the data you put on them! The longest-lasting backup medium still is magnetic tape. If not available, use spinning rust as they still last longer than SSDs when unplugged.


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## ronaldlees (May 21, 2017)

sko said:


> Just as any other flash drive (USB, CF, MMC, SD etc pp) they just die. I have had several pendrives and flash cards that just stopped working after a few years and most of them suffered from bitrot shortly before - the really cheap ones died earlier, the "better" ones (which still use cheap-but-not-THAT-bad NAND) lasted a bit longer.
> These flash drives also suffer from bitrot if not powered over longer periods of time (a few months). They were never ment for backup purposes - never use them as such but back up the data you put on them! The longest-lasting backup medium still is magnetic tape. If not available, use spinning rust as they still last longer than SSDs when unplugged.



I had never read anything about the long-term data viability of NAND storage.  I'll have to look for some more info on this, because I DO have some backup pendrives and also uSD disks that I use for that purpose.

I think the pen drives are more fragile in a "writing while powered off" situation.  I lost a few of them that way, even though they could not have been very close to re-write exhaustion.


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## sko (May 22, 2017)

The presentation from Alvin Cox about this topic back in 2015 made some headlines, but was rather pessimistic and didn't really reflect the actual technical state. This has been analyzed e.g. by anandtech: http://www.anandtech.com/show/9248/the-truth-about-ssd-data-retention

Basically, Cox based his presentation on the general specs for all SSD vendors regarding data retention. These specs require an unpowered consumer SSD to hold data for 1 year and enterprise SSDs only for 3 months. As anandtech shows
So even if it isn't as drastic as Cox had stated, everything beyond the specs is still a grey area and depends on the actual quality of the flash, capicators, storage temperature (and variations) and some other factors. Trying to keep all these variables at optimal values just to find out how far this grey area can be stretched really, REALLY isn't something I'd want to do with my backups...


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## ronaldlees (May 22, 2017)

sko said:


> The presentation from Alvin Cox about this topic back in 2015 made some headlines, but was rather pessimistic and didn't really reflect the actual technical state. This has been analyzed e.g. by anandtech: http://www.anandtech.com/show/9248/the-truth-about-ssd-data-retention
> 
> Basically, Cox based his presentation on the general specs for all SSD vendors regarding data retention. These specs require an unpowered consumer SSD to hold data for 1 year and enterprise SSDs only for 3 months. As anandtech shows
> So even if it isn't as drastic as Cox had stated, everything beyond the specs is still a grey area and depends on the actual quality of the flash, capicators, storage temperature (and variations) and some other factors. Trying to keep all these variables at optimal values just to find out how far this grey area can be stretched really, REALLY isn't something I'd want to do with my backups...



Definitely food for thought.

I don't have a reasonable alternative for the storage, but thanks for the info.  It may be a lifesaver.  From now on,  I'll dump and restore the drives about every two months on all my backups.


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