Your computer's hard drive has crashed and all data has been lost. to safeguard against data loss, you should have

Backed up (make a copy) your data. Depending on what you're guarding against, you'll need the backup to be offsite. If you copied your data to a DVD and kept that DVD next to your computer, what would happen if there was a fire?

One thing that many people don't realize is that the purpose of backups is only to provide data for recovering data.