The 3-2-1 Backup Principle, recommended by US-CERT in 2012 is currently the most accepted and most popular method. The three suggestions are as follows.
3) Make sure there are least three copies of needed data where one is the original and the rest are backups.
2) Use at least two different storage methods, such as NAS, DAS or cloud services.
1) Store at least one backup in different locations, such as a remote cloud service.
Many people may put their data in different hard drives, but data remains vulnerable because that data is still on the same computer. In addition, external drives are also vulnerable because it is likely that external drives may be damaged over time. This makes them convenient for sharing, but ASUSTOR does not recommend as a backup. ASUSTOR also recommends offsite backups because it is possible that onsite backups may be lost as well which include, but are not limited to natural disasters and theft. Therefore, ASUSTOR continues to remind customers to keep good backups according to the 3-2-1 Backup Principle to help prevent data loss.