Disk archival techniques

[Al Kossow]

 > Yep, it's recognised the need to periodically refresh data onto
 > whatever the current favourite media type is.

It is also MUCH faster to do this than to collect the data in the
first place, and if you don't overwrite the thing you copied from
you have another backup (for a while..)

You do need to be mindful of purging copies of bad files of which there
are other known good copies, and you need to make sure that the verified
files have some error detection/correction mechanism to detect silient
copy corruption (failures in disc write caches, etc.)