What lasts longer: Data stored on non-volatile flash RAM, optical media, or magnetic disk?

"See Recommended Backup Media for Circa 2009? on Server Fault.

As for optical media:

DAX Archiving provides some whitepapers, which I have not read. But there's one written by Verbatim, claiming More than 100 years projected lifetime for DVD-R General.

Recently Adrian Wong of Tech ARP by accident found out that ""CD-Rs that were just 7-9 years old were failing at a significant rate"". So: cross your fingers."

"Optical media is good because it's cheap, but I would use magnetic tape.

CDs and DVDs suppose to be readable for 25-50 years but it's very far from the truth. Even if there's no structural damage some badly written DVDs can loose their content in 2 years.

Flash memories do not discharge for many years. However, it's a relatively new technology, so they might not be tested well enough in this respect.

In contrast, magnetic tapes can be read back after 20-30 years and are designed for backup. Very high temperature (e.g. fire) will erase them, but given normal conditions they will remain intact."

"This is when I wish that MiniDisc had caught on, it should out-last any current archival media.

Basically how it works is to write any data, you first have to heat up the media with a laser, and give it a magnetic field. Which means you can't really even use a degausser to erase the data.

It also doesn't have to read the data through a polycarbonate substrate, like CDs, or DVDs or BluRay disks. Which means that you can leave it in the sun without worrying about it becoming unreadable, due to discoloring.

It's a shame that Sony keeps trying to force it's will onto the consumer. The only time they managed to come out on top, is with BluRay, which they only accomplished through making deals with movie makers."

"A flash disk.

I vote 'flash drive' because I know nothing of it, but it appears to have its own USB bus in hardware. Finding hardware in 100 years that will read old data is the problem neglected here.

Magnetic media, when on tape, we were told to 'refresh' (copy over itself, remagnetizing the surface) every three years. Since, I've found floppy disks to be readable decades later. These disks were stored in a well-insulated environment, so the plastic (mylar) stratum didn't expand or contract. Each has its use.

It's the environment that affects optical media. You may notice that CDs & DVDs are actually translucent. Remember, it's light that causes the dye to react. (DVD-RW disks are written by melting xtals and chilling them to a glass: this glass will recrystallize within months.) Further, the stratum is not perfectly elastic, expanding & contracting back with the heat of the day: it is slightly plastic, never returning exactly to the same shape. Avoid temperature variations. I use Taiyo-Yuden lacquer-coated or Verbatim (with LightScribe) for archiving. I may now switch to a flash drive.

This because I'm unclear of the usefulness of a 300 year old DVD, when DVD players have a life from 6 months to 3 years. I can read only mini-floppy disks now because I saved a good drive in a safe place. If you're going to archive with DVDs, save a $40 DVD player. Or, use a flash drive, which comes with its own player.

All the above is irrelevant if you cannot read the data and move it in the future to a new medium and possibly new format. Use a lossless, ISO standard format: newer ones will replace compressed, 16-bit TIFF for photos. Keep track of new, popular software formats and hardware media; and transfer your family photos as these become available. As with magnetic media, you need choose your file system on a flash drive: the source code for Linux ones are published. The flash drive is unique in having a player with no moving parts.

Consider that a programmer can use source code published in paper libraries or on internet archives to re-write old file systems and read file formats. But it would take a very clever engineer to build a device for reading the medium; unless its just electronics to convert USB in the distant future to 'Microsoft Protocol' protocol, & software to convert ext3 to 'Microsoft Format' format.

Although the Wikipedia gives newer EEPROMs a 10-year life, this quote is interesting:

'Channel Five's Gadget Show cooked a flash drive with propane, froze it with dry ice, submerged it in various acidic liquids, ran over it with a jeep and fired it against a wall with a mortar. A company specializing in recovering lost data from computer drives managed to recover all the data on the drive.[22] All data on the other removable storage devices tested, using optical or magnetic technologies, were destroyed.'

http://en.wikipediadotorg/wiki/USB_flash_drive#File_system

Because a simple USB dongle can now hold as much as 55 DVDs, and the USB bus will likely outlast DVD players or tape drives, a flash disk is the clear choice in archiving data. (Get another with a write switch for holding a bootable repair & malware extraction kit; get another that stores encrypted incremental backups & take it home each night.)

Bruce Bathurst PhD

PS. To support my research in petrology, I took jobs in all aspects of computing. For each client, I chose the best tools for that particular business. Thus, I don't feel biased in my conclusion. In fact, I've never even used a flash drive! :-)"

"There are a number of issues - first is the stability of the media itself. Floppy disks here in Hawaii rot due to high humidity/mold/mildew issues. I've seen so much media destroyed that I'd say if you can't guarantee low humidity, mag media is out.

The second thing is the media format - who can read 5-1/4"" floppy disks? 8"" floppy disks? Even the Zip 100 disk drives are getting few on the ground much less the older tape formats.

The third thing - what encoding are you using for the data? If not a standard and hopefully open standard format, then you may not be able to even get it understood. Even Microsoft Office has problems reading Microsoft Works on occasion, much less something like more obscure formats."