How does it fail: CD/DVD/Blue-Ray

Optical media is still a popular form of backup, and for a good reason: It is cheap and lets you keep the copy "forever". But what is that? In general you should not count on a burnable optical media to last for more than 5 years. The chemistry is changed all the time, and the media are made for practically no money in all sort of far east countries, so you really does not know what you got.

The most common ways to destroy optical media is time, sunlight, heat, moist and scratches. Keep it dark, dry and at a stable temperature, and it will last longer, but don't count on it.

How it fails: Online and cloud backup

Online backup, often named by the buzz word "cloud", is when you have a program upload your data to a company that will keep it safe. When you needs the data you can download it. This is very easy because the program pretty much takes care of itself, and you get a real offsite backup.

This sounds perfect, and when something does that you can know it is not:

• Companies goes bankrupt - online backup companies does too and even though your data exists the servers are turned off.
• Data loss - all the usual ways of losing data applies to these companies too. They may have better safety but not 100%.
• Got a new credit card? And did you forget to update the number with your online backup? And maby the contact e-mail address was outdated. You might not notice untill it is too late.
• You lose the password or encryption key for the backup, you lose it all.

By the way: All of these scenarios has happened within the relatively few online backup has existed.

Online backup or cloud backup

With todays fast and cheap internet connections it is very popular to make a backup to "the cloud". It usually works like this:

• The backup company provides a program which you install.
• You tell the program what to backup and lets your computer run until all of the data has been uploaded.
• From now on the program will only upload the data that changed, which is usually very little.

One thing to look for, is if the company has a separate restore price. When you have lost your data, it is not fun to find out that you must pay a horrible rate to get your data back. Restore should be part of the subscription.

How does it fail: RAID

Because harddisks fail often, it is possible to use multiple harddisks together, to get better safety.

RAID is short for Rapid Array of Inexpensive Disks. It will manage multiple disks and let the computer think there is only one disk. There are in general 3 different kinds of RAID in use today:

RAID 0: Scary raid, never use this! This just makes multiple disks look like a big one. Often reading and writing speeds are higher, because multiple disks can be read and written at the same time. But if just one disk fails, you loose all of your data. This makes the disk of loosing data much higher so never use it! Todays disks are so fast, that there is no practical use of RAID0.

RAID1: Usually used with 2 disks but it only has the size of 1. What you get is 2 disks which always have the same data. One can fail, and your system will keep running. This is the most secure form of RAID, but it is not 100%. When one disk has failed, you have no backup until you have replaced it and there are many examples of data being lost in this time span.

RAID5: Used with more than 2 disks, e.g. 5. Only 1 disk is used as backup, so with 5 disks you have the space of 4. As with RAID1 you loose your data if 2 disks fail at the same time and because you have more disks the risk of this happening is greater.

RAID5 works using "parity". Lets take this calculation: 1 + 2 + 3 + 4 + 5 = 14. If you replace any of these numbers with a ?, it is still easy to derive the missing number, e.g. 1 + 2 + 3 + ? + 5 = 14 <=> 14 - 1- 2 - 3 - 5 = ? = 4.

Finally, there is also the risk that the hardware or program which controls the RAID breaks down.

All in all: RAID fails in the same way as harddisks, just not as often. But it does happen, even with very expensive enterprise systems.