Tools that may be used to back up data include small flash-based USB, CDs, DVDs, external hard drives for PC users. However more sophisticated techniques are needed for larger organizations such as insurance companies and banks.
The tools to choose depends on the size of the files to back up. For example files of 200 to 400 MB (approximately 400,000,000 bytes) may fit in a CD. However files of 3 to 5 GB (approximately 5,000,0000,000 bytes) fit into a DVD. For larger files with tens of GB, external hard disk drives (hdd) are necessary.
All the above storage devices such as USBs, CDs, DVDs and HDDs are fragile and breakable hence the need to more than one back up copy kept in safer places.