Stability of Flash Memory

Factual Questions
1

If I were to backup a file set by burning a data CD/DVD, writing to an external hard drive, and writing to a Flash drive, and then stuck all these in a closet for some number of years, undisturbed with stable temperatures etc, which media will be readable for the longest time? How soon will each deteriorate and be unreadable?

I’ve googled this a bit, and I think I have a good handle on the first two, but I haven’t found data on long term flash memory reliability; googling brings up a series of abstracts for engineering papers, and not much else – no actual data from manufacturers or testing bodies that I could find.

What’s the scoop?

2

From a purely speculative viewpoint, I’d say that USB ports, or mechanics to connect to USB ports, will exist for quite some time. We’ll need ways to connect external stuff to a main computer, and USB’s seem to be the way to go.

CD readers will probably go the way of 5-1/4" drives and Zip drives, as they are bulky and easy to break. Flashdrives make transporting data a lot easier, and much more reliable. Heck, I’ve washed my flashdrive in the washing machine twice, and it still keeps on going. I’d hate to see what happens to a CD if you wash it.

An external hard drive, provided it has a usb port, will probably last as long as a flash drive. However, since the hard drive depends on moving parts, I’d give them a lower life span than the flash drive, because the flash has no spinny parts.

As to how long they will last - In a stable environment, your guess is as good as mine. :slight_smile:

3

Well, I guess I assumed that USB would be around a very long time – some PC’s still have RS-232 ports. Hell, my workstation has a parallel port!

Let’s say USB will exist for 10 more years (what the hell), and I stuck in the same closet a shrink-wrapped USB CD/DVD reader, just in case aliens steal all the optical disk readers one night. So its a given (for this thread) that the interfaces for those three formats will exist for a decade or more. The question is: which of the media will still work when you plug it in, and for how many years?

ETA: I’d guess that Blu-ray drives for PCs will still be reasonably wide spread 10 years from now, and these can currently read data CDs and DVDs.

4

I wouldn’t necessarily trust just any old optical media

I don’t have a cite but there’s quite a few non-volatile solid state storage technologies with expected data retention of over 100 years.

5

Isn’t Flash memory a non-volatile solid state storage technologies? I’m asking what’s its expected data retention is.

6

Well, twenty year old flash drives currently have no data recovery at all. So, it is all speculation. Magnetic disk drives twenty years old do exist, but reliability is still a “mean time until failure” estimate where the variability is greater than the magnitude of the time being measured, which is less than forty years for almost all iterations. Gold will supposedly increase DVD, and CD lifespans to fifty to one hundred and fifty years. That too is an estimate, and that estimate comes primarily from the folks who manufacture and sell the disks.

Vinyl records from eighty years ago are fairly rare, and data retention is difficult to estimate, since the original recordings were less than perfect, but even the original Ediphone cylinders are playable today, if maintained in museum quality storage.

For hard core critical data security applications, multiple site dynamic verification and duplication by schedule is the only really reliable method, and even that has some risk, since almost perfect is imperfect. While it may be true that the laws of entropy require that information cannot be destroyed, it does not guarantee that information will always be retrievable.

Well protected DVD’s, in archival gold, in constant temperature will probably give you the best cost per decade per gigabyte results, but flash drives are adequate, over probable use periods. Storage greater than decades will undoubtedly be best served by dynamic retrieval and and archive to “modern” media when available.

Tris

7

There’s twenty year old flash drives? Color me surprised. Or perhaps you were making a joke?

Sure, but I haven’t seen much speculation on flash drives’ endurance, even from manufacturers. Weeks? Years? More? I’m sure this is out there somewhere, but my google-fu isn’t digging it up.

Sure, of course. But MTBF is measured in hours of use, no? If the drive is unplugged in my (magical, sealed, thermally constant) closet, does MTBF even apply?

Ok, that’s good to know. Thanks. I do wish I could get some timescale for flash storage, though. It sounds like you’re saying it should be similar to the best DVD-gold storage under optimal conditions?

8

Here is an engineering note from Freescale Seminconductor on the estimated data retention of their non-volatile memory. All of them are >100 years.

Edit: To be clear, this seems to apply to program/data area storage in their micro-controller line. I do not know if Freescale makes any sort of dedicated high capacity storage IC incorporating the same technology. However, this shows that it is at least possible, even if it’s not available.

9

The OP seems to be about the absolute lifetime of the medium, but the practical answer depends not merely on the medium’s stability.

Let’s say that a disk or flash drive has survived undamaged and undegraded for 100 years. To recover that data, you will need working hardware and software capable of reading the stored data. It is not safe to assume that such systems will still exist or be easily replicable decades from now.

There are many forms of magnetic storage (e.g. computer data tapes and disks, various video tape formats) from the 1950s and '60s which can now only be read by antique hardware carefully maintained in working condition. As time goes by, these machines fail and ultimately there is no longer any way to recover the information on any remaining media.

So if you really hope to access your data, you had better put all the of the hardware and software necessary to read it in archival storage in your closet, along with the data. To be completely safe, you had better include detailed technical manuals for every component and piece of software.

BTW, most archivists agree that the best options for long-term information storage are analog, not digital. Documents on acid-free archival paper can survive hundreds of years. For motion pictures, color separations on B&W film can last more than 100 years.

You mean because they were only invented 13 years ago?

You mean non-existent, since they were invented in 1948? (78 rpm records were made of shellac, not vinyl.)

10

Some clarification.

Sorry about the vinyl. wasn’t even thinking of the media, more the method.

Flash drive data loss comes from two major areas. Read write process which depends on use is one source, and eventually, multiple reads, multiple writes, or erases will cause failure on a bit by bit basis. Recent developments in the technology might have reduced that by significant levels, but only time will tell, and the first ones using the new technology are barely on the market.

Discharge from incedent electromagnetic radiation is another source. Since that includes even cosmic ray bombardment, it is only partially amenable to mitigation by shielding. It is a slow, but inevitable source of errors. Decade long storage without use is probably a reasonable expectation, and this is especially so in data that are forgiving of single bit errors. (JPG, MP3, MP4, and similar data)

Both of these types of loss are also present in DVD disks, but are likely to be much lower in overall rates, except in highly controlled storage environments. (it takes more energy to alter the bit on a film, than in a chip.) For this reason, disk manufacturers are pretty secure in their multi-decade predictions. Stored, and protected, DVD’s are much cheaper per bit than flash drives.

Mechanical systems, which are prone to other causes of failure would be an additional source for magnetic disk drives. The actual plates have a slightly higher loss rate than DVD formats, but read processes by mechanical systems are much more prone to large volume data loss, over long term storage. It turns out that drives that have been shelved are only slightly more reliable than drives that have been used, for multi year long periods.

The lighthearted report about twenty year old flash drives was intended to highlight the fact that the entire duration of digital data storage, of all types is less than the expected lifetime of a book, in your livingroom. Estimates of centuries, still fall short of print media, many of which have lasted three or four hundred years, and some much longer. (Consider the Dead Sea scrolls, or any of thousands of Egyptian inscriptions.)

You want to save your music, or your photos, DVD’s will probably work for your lifetime. If you want to bury them in your Pyramid, maybe not.

Tris