Any system for re-using backup mEDIa, e.g. magnetic tape. One extreme would be to use the same mEDIa for every backup (e.g. copy disk A to disk B), the other extreme would be to use new mEDIa every time. The trade-off is between the cost of buying and storing mEDIa and the ability to restore any version of any file. One example is the Grandfather, Father, Son (GFS) scheme. (2004-10-08)