memory

September 7, 2007 10:40 AM

How long can a hard drive store data ?

I dont know if this has been asked before - but how long can it store memory/data ?
Say i have one jpg or raw file on a hard drive - i take it out of the computer and store it in a cupboard - how long could i leave it in ?

posted by sgt.serenity to technology (11 comments total)

Google has an interesting paper on drive failures: Failure Trends in a Large Disk Drive Population
posted by smackfu at 10:54 AM on September 7, 2007

Data on this is tricky because failure data on hard drives generally looks at failures in working drives (i.e. data is constantly written/overwritten) rather than the media as an archival format. I doubt there is much empirical data on this question. I'd guess it would be in the vicinity of other magnetic media - 10-30 years? 50 on the outside? The issue of whether anything is going to be functionally "readable" in that sort of span is well taken as well - in this day and age data maintenance has to replace the concept of data storage (i.e. you must constantly rerecord and upgrade data into a current format).
posted by nanojath at 11:04 AM on September 7, 2007

"All magnetic storage media has a finite life because magnetic fields start to decay as soon as they are written. This means a tape or drive will not retain its data forever. In a proper storage environment, it's reasonable to expect that the drive should remain readable for up to 10 years. The concern is more about the drive's mechanical reliability; will it physically spin up? After a very long period of disuse, the spindle bearings or head actuator may be stiff, resulting in read/write errors."
posted by zeoslap at 11:06 AM on September 7, 2007

What about flash memory? Has there been any tests on that yet? Being its not magnetic nor have any parts to fail... could it last infinitely?
posted by wile e at 11:39 AM on September 7, 2007

I have a couple external hard drives; I've been told to move to a newer medium the really important stuff -- say, important photos/mementos -- every 3 years. 4 maximum.
posted by matteo at 11:48 AM on September 7, 2007

Depends. If you are willing to pay a company to extract the data you might be looking at the 20+ years range. If you just expect it to spin right up you're looking in the less than 10 years range. In the case of the former, how you store it is probably the biggest factor. In the cupboard? Not so long. Climate controlled sealed environment? Probably very long.
posted by damn dirty ape at 11:49 AM on September 7, 2007

DDA: The hard drive case itself should be sealed. And I wouldn't imagine there would be too many temperature shifts in a cupboard.
posted by delmoi at 11:57 AM on September 7, 2007

@wile e: Flash memory "forgets" over time as well. The way it stores bits is in millions/billions of capacitors.¹ Since the capacitor's dielectric isn't perfect, it 'leaks' charge over time. Over the very long term, the charges will deplete completely and the card will be empty.

I'm not sure whether (nor am I sure if anyone knows with 100% confidence) whether the decay time of the electric charge that represents the data in a Flash device would be greater or less than the decay time for the magnetic hysteresis that stores the bits in a hard drive or tape.

I've heard anecdotally that magnetic core memory, of the type used in some older minicomputers, was very long-lasting, since it was magnetizing a fairly large chunk of ferrite for each bit. I had a geologist tell me once that based on how long it takes for similar magnetic fields to dissapate in rocks, that the "bits" would still be there for thousands of years...if you could figure out a way to read them. (And that's a real trick, because the read process on a core memory system is destructive.)

Based on what the manufacturers claim, I wouldn't trust a hard drive or Flash device out beyond about 10 years. Very good CD or DVD+R media might be good to somewhat longer.

Pressed (commercially manufactured) CDs are probably good for a very long time, since the data there is being stored physically rather than chemically, electrically, or magnetically.

1 - Yeah, I know this is a gross oversimplification. But capacitance is the key concept that lets you store data in either a NOR or NAND gate; without the 'floating gate' the whole thing wouldn't work.
posted by Kadin2048 at 1:07 PM on September 7, 2007

"DDA: The hard drive case itself should be sealed. And I wouldn't imagine there would be too many temperature shifts in a cupboard."
posted by delmoi at 2:57 PM on September 7 [+] [!]

Hard drives are most certainly not sealed. All commercial drives have an air exchange port, usually a hole the diameter of a paper clip, that can't be blocked, for normal operation. That's because a hard drive's heads "fly" on a thin cushion of air created by the rotating platters. It's also the reason why hard drives have altitude limitations; at high altitudes, the density of air drops to the point where the cushion of air created is insufficient to keep the heads flying.

Hard drives are optimized for data density, not archival storage. The recent move to perpendicular recording technology has been very good for increasing storage density, and lowering storage cost, but it has also probably helped archival life, as the thicker media coating, and the higher stored domain strength both favor better long term data life. So, more modern drives may do better in the long run, than older designs.
posted by paulsc at 1:41 PM on September 7, 2007

matteo writes "I have a couple external hard drives; I've been told to move to a newer medium the really important stuff -- say, important photos/mementos -- every 3 years. 4 maximum."

That's more about the reliability of the mechanical portions of the disk.

For curiosity sake I plugged the oldest hard drive I have hanging around into a machine. It's a 124MB Maxtor manufactured in 1995 that I last used in '97. Once I got the CHS set it worked fine, all the data was still there. Mind you older drives had bits much larger than those found on modern drives. Disks are probably better than tape because tape suffers from a failure mode where the overlapping layers degrade each other.
posted by Mitheral at 8:07 PM on September 7, 2007

It's standard advice to take old floppies out of storage every few years and rewrite them. The media degrades very slowly, but the magnetic domains fade somewhat faster, and especially on old drives that fell out of alignment if you looked at them funny, reading the media while it's still good and strong is a good idea.

Likewise on hard drives, rewriting the data every year or two is probably a good idea, except for one problem: The servo data, which allow the head to position itself over the platter, aren't writable by the drive after it leaves the factory, so when they fade, you're done, period. (except for the expensive data-recovery services already mentioned.)

However, drives get so cheap so fast, just buy a new $80 drive every 5-7 years and copy the data onto it. That'll also help you keep up with interface obsolescence, which wasn't an issue with IDE's 20-year reign, but I don't think SATA will be around that long.

Choice of filesystem and data format become important at these timescales, too. How are all those WordStar or GeoWrite documents doing? Today's XML is tomorrow's EBCDIC.
posted by Myself at 9:28 PM on September 8, 2007