One of the ways to backup your data is to copy your entire disk to another disk. Naturally this is called disk to disk backup. Compared to backups made to tape or other media, disk based backups are faster, more easily restored and disks have become so cheap that every one can use them.
 
Depending on the storage system, backup times are noticeably and even dramatically shorter than those required for tape backups. In many companies, this technology renders the backup window a lot smaller. The outcomes being that backups are more up-to-date, since they can be run more frequently, while application and backup servers become available more quickly for other tasks and are under less strain.

The cheapest way to backup your data is to use external devices like CD/DVD or USB drives.
Let us consider the features of the external media currently available:

1. CD-ROM Disks: One of the cheapest backup media available, the CD can store about 700 MB of data. One can easily store data on a CD with the help of CD-writers which are common in most computers available today.
2. DVD-ROM Disks: These are a bit costlier than CDs but considering that one DVD disk can store 4.2 GB of data; the cost per GB is less as compared to CD.
3. USB Drive: Falling memory prices have made these backup media very cost effective. The additional advantage of these drives is that they can be reused many times unlike the CD/DVD. The only drawback is that usually a USB drive is required on the computer which may not be present in all computers.

Tapes are the earliest forms of data backup. A tape media consists of a long flexible ribbon made of flexible plastic coated with magnetic media. The tape is wound on spindles and stored in mechanical cartridges that protect it from dust.
 
Backups made to tape media are mostly used in corporate environments due the following reasons: