[BBLISA] Whatever happened to Seagate?

[Edward Ned Harvey (bblisa4)]

> From: nahamu at gmail.com [mailto:nahamu at gmail.com] On Behalf Of
> Nahum Shalman
> 
> Whatever the shelf life, my only concern was that anyone truly
> ditching HDDs in favor of SSDs should be aware of the differences and take
> the appropriate precautions accordingly.

This is a good point - but remember that even tapes, hard drives, and optical media all have shelf lives, because they're all chemical and/or electric states on a microscopic scale, that will deteriorate.

There is very little data out there about archival shelf life for any of these media - tapes have the most information available, and even *that* can be difficult to find, and/or inaccurate. 

For magnetic material, the degradation is "self-demagnetization" which occurs when adjacent bits oppose each other, and slowly cause one or both bits to neutralize each other.

For nand flash material, the degradation is caused by a leakage current, causing the floating gate to slowly lose its electric charge over time.

For optical material, I don't know why or how the phase change material degrades over time, but I know I've used a lot of them, and have periodically gone back to read and verify media over time, and have found it degrades very quickly - Around 20% of burned DVD's go bad in about a year.

For both magnetic material and flash material, the way to refresh the data is to read and re-write the data to the medium periodically. And store redundancy and cksums. That way, as the bits *slowly* deteriorate, you're still able to get reliable reads from it, and each time you write, you're storing fresh bits in their fully un-deteriorated state.