The 3-
This backup strategy should be followed for all important files and documents.
If you even only slightly care about losing access to any piece of information, then it is important and it should be backed up!
3. There should be 3 copies of any important files (a primary and two backups).
From an business viewpoint, this could be on a local hard drive, an external drive or a NAS drive and a tape based archive. Other possibilities could include USB keys, optical media like CDs and DVDs or even cloud based storage. Whatever, there must be at least three different and distinct copies of the files.
2. The files should be kept on at least two different types of media.
Businesses are likely to use hard drives and tape, but CDs and DVDs, USB keys and cloud based storage also count as different types of media.
1. At least one of those copies should be kept offsite (or at least offline).
It seems obvious, but if something happens to the server your data is on, your backup could be similarly affected. One of your backups should be kept at a different site. For a business, this could be a secure site where your NAS is located, or where your backup tapes are kept. It could even be a cloud based storage service.
3-
While the 3-
Do consider USB hard drives, NAS drives and cloud based storage strategies.