|RAID may provide varying levels of protection against some forms of mechanical failure. However, there are electrical and mechanical failures that could cause the loss of data. There is no substitute for backups. Catastrophic loss of an entire system or even building can also happen. That is why offsite store exists.|
If you are thinking along the lines of PCs then the amount of personal (irreplacable) data that needs to be backed up is managable by a number of means.
I prefer optical media because I believe it offers the best long term solution an is also the most cost effective approach. Especially if you consider multiple copies of a backup set.
Using flash media for backup purposes is the riskiest of all possible choices IMO. That media has limited rewrites, is cheaply fabricated, subject to loss or theft. All that in addition to the other risks mentioned above.
Backup and imaging are cousins that are referred to interchangeably. I may get some dissension on this point but I feel there is a distinct difference.
Backing up simply means copying. That can be the entire partition/drive or just portions of it.
Imaging usually refers to creating an exact copy of the original. Imaging usually is accompanied by some means of compression too.
Imaging is what Ghost and Acronis true image do. By compressing the data you allow more data to fit into a smaller storage space. However that data is readily readable. It needs to be restored. That can be done to the original location or a new location.
Backups on the other hand are usually just copies that can be readily accessed.
You need to immediately make copies of all your personal files as you create or collect them. Then occasionally you can image the partition to be able to restore an exact copy of ALL the original files. That is done more for convenience and time saving than data protection.
Newer versions of Acronis products allow incremental backup/imaging.
Finally, an external hard drive is a better storage device than none but remember the same failures and other risks that can happen to your internal drives can also happen to your external. Additionally, the enclosures are prone to failure and can cause drive overheating.
I use a combination of Drag to Disk, External USB hard drive and DVDR media images created using Ghost 2003.