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Backup and Recovery, the 3-2-1 (-1) Model

The 3-2-1 backup is a reliable recovery methodology for ensuring that data is protected adequately, and backup copies of the data are available when needed. The basic concept of the 3-2-1 backup strategy is that three copies are made of the data to be protected, the copies are stored on two different types of storage media and one copy of the data is sent offsite.


In the classic 3-2-1 backup scenario, backup software makes a copy of the company’s critical data and saves the copy to another on-premises storage device. During that process or immediately afterward, two more copies of the data are saved to two other devices—traditionally at least one of those devices was a tape library. Tape was a standard part of the process because it made it easy to create a portable copy of the data in the form of a tape cartridge that could easily be sent offsite.


Although the 3-2-1 backup approach has been around since the early days of data protection, it is a concept that is still embraced by most backup software and hardware vendors as a best practice for using their products effectively. They recognize that the general concept is still valid regardless of how or where a company stores its data, even as new requirements and voluminous data have made the 3-2-1 equation a bit more complicated.


3-2-1 backup rules

The 3-2-1 backup strategy is made up of three rules, they are as follows:

  • Three copies of data- This includes the original data and at least two backups.
  • Two different storage types- Both copies of the backed up data should be kept on two separate storage types to minimize the chance of failure. Storage types could include an internal hard drive, external hard drive, removable storage drive or cloud backup
  • One copy offsite- At least one data copy should be stored in an offsite or remote location to ensure that natural or geographical disasters cannot affect all data copies.


The 3-2-1 backup strategy is composed of three steps in descending order.


Importance of the 3-2-1 rule

The 3-2-1 backup strategy is recognized as a best practice for information security professionals and government authorities. While it does not guarantee all data will never be compromised, this strategy eliminates the most risk. The 3-2-1 methodology is important in ensuring that there is no single point of failure for data. Not only is an organization covered if one copy is corrupted or a technology fails, but also if a natural disaster or theft occurs that wipes out the physical storage types.


Variation on the 3-2-1 backup methodology

There are a number of ways of achieving a workable 3-2-1 backup system, and the variations on the basic theme will depend largely on the amount of data to be protected, the installed storage equipment and the type of offsite repository available.


For example, the first step of making the three copies of the backup data can be accomplished in a variety of ways. The simplest method would be for the backup software to create the “master” backup copy and then that software or a replication utility would make the two additional copies, storing one on a different media type. Alternatively, mirroring could be used to create the first two copies simultaneously with the third spun off from one of those copies. Because one copy has to reside on a different medium, the process of making that copy is often the final step in the process as copying to a different media type is likely to occur at a different rate than that of making the first two disk or solid-state drive-based copies.


For the second copy that is maintained in-house for quick or operational recoveries, companies should store that copy on another server or storage system separate from the originating equipment. The target gear for the second copy should allow easy access to the backup data in case it is needed, such as if the original data is lost or damaged. Storing copy number two on equipment similar to the original system should facilitate recoveries.


However, the in-house copy does not necessarily have to be stored on the same or similar media. In some cases, an organization may make the first “master” copy and then copy that data to two tape drives, simultaneously or sequentially. One tape cartridge would be retained onsite and the other would be sent to the offsite facility. The drawback to this approach is that recovering data from the onsite tape might take some time, certainly longer than recovering from a hard-disk or solid-state drive. This would also be true if other types of removable media were used, such as optical disks or removable drives, although recovery times will vary.


Some backup software applications will handle the multiple-copy aspect automatically, possibly even creating the second or third copy. Data duplicating or replication applications can also handle this chore. In very small environments, the second and third copies may be triggered manually, but that method quickly becomes untenable as data stores grow.


Getting the third copy offsite

In the traditional version of 3-2-1 backup, satisfying the requirement that the “1” copy of data must go offsite was typically accomplished by sending a tape to another location. Usually, a company would contract with a tape vaulting service, which would pick up and store the tape cartridge. Data copied to non-tape portable media would similarly be handled by an offsite vaulting service.


Today, many companies still rely on tape and outside vaulting services, such as Iron Mountain. Some companies that have their own remote facilities such as secondary data centers or disaster recovery installations may use ordinary courier services to pick up and deliver their offsite copies.


Vaulting or other offsite scenarios come with their own caveats. Too often, tapes get lost between the loading dock, the delivery van or the offsite service. And natural elements—heat, cold, rain or snow—can wreak havoc with tape cartridges, causing data loss. For these reasons, offsite copies on any medium should be tested to ensure their integrity soon after they arrive at the remote facility.


Increasingly, however, companies are trying to avoid the pitfalls of manually handling copies of their data by transmitting their offsite copies electronically. So instead of physically shipping tapes, disks or drives, offsite copies can be sent over the internet or private communications lines to a cloud storage service. Often, the backup software or hardware will handle transmitting the offsite copy automatically.


If the offsite copy also represented the second media type copy (the “2” of 3-2-1), sending it to a cloud service adds a wrinkle to the 3-2-1 backup method as the service is likely to store the copy on the same type of media that is used in house. Although this deserves some consideration, it may not be an issue, as cloud storage is often considered more of a storage medium than an alternative storage location.


Universality of the 3-2-1 backup rule

Data protection technologies and techniques have evolved considerably since the 3-2-1 backup methodology was first conceived, but it can still be applied to the various forms of modern data backup and recovery.


Snapshotting and replication are two widely used data protection technologies as they help overcome some of the obstacles of adequately backing up very large data stores. But using snapshots plus Replication fits nicely within the 3-2-1 model as the methods used to make the original copy of the data as well as the two duplicates.


Backup appliances are relatively new fixtures in some data centers that combine backup software with dedicated hardware. These devices simplify initial backups and can usually connect seamlessly with a cloud backup service to stash an offsite copy of the data.  Similarly, data protection processes like continuous data protection (CDP) strain the 3-2-1 model a bit, but with proper management these newer approaches can support 3-2-1 effectively.


New uses of backup data and the 3-2-1 rule

There are other developments in modern data protection that do not eliminate the possibility of using a 3-2-1 backup scheme, but they may make it a little more complicated to manage. Two of the most impactful developments involve using backup data for other purposes and the shifting ideals of data integrity.


Today, backups are not just insurance policies, tucked away until something goes awry. Companies are extracting more value from their backup data stores by using that data for things like developing and testing new applications. Contemporary approaches to programming, such as DevOps, require easy access to data that is as close to the real thing as possible to ensure that applications are developed properly. Backup data fits that bill very nicely.


Analytical applications may also need access to large amounts of current data. By using fresh backup data, the results of the analytic process are likely to be more reliable and accurate. Tighter controls and management of data companies is required to ensure that these applications get the best data possible while maintaining the primary concepts of 3-2-1 backup.


Data integrity has always been a key concern of data protection activities. It is not enough to simply back up data and lock away the copies, it is imperative to ensure that backups are complete, uncorrupted and recoverable. Recovery testing helps in this regard, as well as employing some of the more advanced features that backup apps offer to detect ransomware and other threats. Again, these concerns do not necessarily derail a 3-2-1 backup approach, but they may add some steps to the process.


The GDPR—General Data Protection Regulation—is another contemporary wrinkle that could affect data protection practices. The GDPR is a European Union enactment that defines the steps that organizations must take to protect the data of its users. For 3-2-1 backup practitioners, this means ensuring that wherever those three copies of data are stored, security measures are adequate enough to ensure against data loss and to avoid potentially crippling EU fines.


Another directive of the GDPR says that a company’s customers or users have the right to have their names and all data related to them expunged from the company’s storage systems and media. In a 3-2-1 environment, this means that the information must be removed from all three copies of the data.


Shortcomings of 3-2-1 backup

As an effective data protection scheme, 3-2-1 backup has stood the test of time, but when in the context of contemporary storage systems and services, some of the steps and practices may need some adjustments.


Keeping track of 3-2-1 backup data copies can get complicated depending on the type of backup an organization is using in its 3-2-1 setup. For most companies, doing a full backup daily is not feasible, so other approaches are likely being used, such as incremental or differential backups. Because those types of backups require some interim actions to produce a full backup copy, the “3” data copies part may require some added management to ensure that all available copies are up to date and easily accessible.


If a cloud storage service is being used to store the offsite copy, the service provider should be asked to provide details related to its data protection processes. Also, many cloud storage providers will charge customers extra to recover any data that the customer may have accidentally deleted. To avoid over charges and to add a level of data safety, it is a good idea to copy the cloud-based backup to another cloud storage service.


As noted earlier, using a cloud storage service or transmitting a backup copy to a remote facility requires telecommunications services with ample bandwidth to handle the volume of data that is being sent or retrieved. These costs may also escalate as the amount of data a company has grows. And even with speedy communication lines, it takes time to retrieve data, so that should be considered when developing recovery plans.


If tape or optical libraries are part of the 3-2-1 backup scenario, to ensure that data can be recovered in a timely manner, it is necessary to maintain that equipment. Generally, that should not be an issue, but if a company uses tape or optical gear that is older or even end-of-life, maintaining that equipment appropriately may be difficult or costly.


3-2-1 backup management

There are some basic managerial fundamentals for a successful 3-2-1 backup implementation, including:

  • All data copies are identical and up to date.
  • The media that copies are on is readable media.
  • All copies and equipment are tested and confirmed to be in working order.
  • Remote copies are stored safely.
  • Plans to recover single/multiple files or a full backup have been tested.
  • Internal data copies are on different storage systems and networks and are not accessible from outside the company.


The backup software used in the 3-2-1 process can be very helpful as it can automatically direct the disposition of backup copies while cataloging all backup activities. Most backup apps have also added features to check for threats such as malware, ransomware and viruses in backup copies.



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