On Wed November 30 2011, Klaus Knopper wrote: > Also, flash media ages. Manufacturers only guarantee cells to hold the > information up to 10 years, so, flash is probably not good for long term > storage. Well... Similar problem for magnetical or optical storage, > which make it up to 50 years only. Printed paper lasts much longer. But > that is a different topic. ;-) >
Mostly I agree but would like to add a bit of detail because all too often people look at tomorrow or next week, not next decade. Flash media cells are indeed often quoted as having 10 year lifetimes. I don't have any old enough (yet) to check but one must be careful of the English language here. ;-) Useful lifetime != length of time until a significant error rate develops among the large group of cells holding your 200Kb novel. Your flash devices should probably be re-written on a regular schedule, maybe once every 3 to 5 years. I have a small handful here, approaching the 3 year power-off point that I will be testing in a few years from now. Just to check my guess. Iron oxide films - such as in magnetic tape and flopply disks (quoted at 10 year retention times) need to be read and re-written at least every 3 to 5 years if recorded with ECC. More frequently if not recorded with ECC. Note: A number of years ago NASA found themselves painted into this corner. They had more data recorded on mag tape than was possible to read and re-write to optical storage in the retention time of the of the magnetic media. Opto-magnetic recording media (with ECC) where quoted at 20 years. I do have some approaching 15 years, power-off. May need to check those RSN. ;-) Optical media (common CD, DVD, single layer - all have embedded ECC) have often been predicted to have a 50 year lifetime. But they haven't been around a significant enough portion of that time for this number to be more than a wild guess. Personally, I haven't found any errors in mine that are approaching the 12 year mark. So far, the winner is (other than physical volume) punched paper; Either cards or tape on media that was intended for archival storage. Most of that which I have is approaching 50 years, and those little holes are still there. It is nice to be able to see each bit. ;-) Right now, if you need long term data storage, your best bet is to use "archive quality" paper and ink, print in bar-code (or similar) digital patterns, store in a temperature controlled dry nitrogen atmosphere. You should be able to get 200 to 300 years without needing to re-write the data on new media. - - - - O.T: Klaus, this thread reminded my I hadn't tried Knoppix in awhile. I downloaded 6.7.1 to a DVD yesterday and then flashed to a UDMA, CF disk - all works great, thank you. Mike ------------------------------------------------------------------------------ All the data continuously generated in your IT infrastructure contains a definitive record of customers, application performance, security threats, fraudulent activity, and more. Splunk takes this data and makes sense of it. IT sense. And common sense. http://p.sf.net/sfu/splunk-novd2d
