Most manufacturers claim their flash drives will retain their contents for at least 10 years, but there are a number of variables that can shorten that time span.
If the flash drive was new when you copied the data onto it, it should be safe for at least most of those estimated 10 years.
If the drive was used however, I wouldn’t count it it lasting more than one-half to two-thirds of that time. Also, keeping the drive stored in a cool, dry location will help maximize the life of the data stored on it.
If your data is really important to you, I would back it up onto a second USB drive and give it to another family member or a trusted friend (who doesn’t live in the same house) for safekeeping. And after a few years you can transfer them to a new USB drive.
That way if one drive becomes lost, damaged or simply stops working you’ll have spares tucked away that you can use to retrieve those precious files.
Better yet, you could buy several thumb drives and hand them out to various trusted friends and relatives. After all, they are quite inexpensive these days.
A couple of other long-term storage options that I recommend are burning your data onto blank DVDs and/or uploading them to the cloud or one of the many free online storage services that are available these days.
When it comes to safely storing files that you simply cannot afford to lose, it’s wise to always do two things:
1 – Store at least one additional backup in another physical location.
2 – Keep multiple backup sets (in the form of USB drives, external hard drives, DVD’s or online cloud storage services).
Source: Rick’s Daily Tips