Anyone who begins looking into the various different backup technologies available today, will soon discover that not all backup software is created equal. The three most commonly encountered technologies are Disk Imaging, File Based Data Backup, and File Synchronization. Many people are confused about the differences between these, and rightly so because the software employing these technologies often overlap somewhat in function.
I remember someone saying to me once, “Well, backup is backup. Right? It doesn’t matter how you do it, as long as you do.” It is true that doing some sort of backup is better than doing none at all, but there good reasons why different backup methods exist. No one type is meant to be a complete replacement for the other. I believe the different technologies complement rather than compete with one another. In the paragraphs below we will be looking at each of the major types of backup software, what their primary purposes are, and their advantages.
This type of backup is often described as a “bare metal backup” because it backs up physical disks at the volume level. In other words, a true disk image is an exact copy of an entire physical disk or disk partition.
In its simplest form a disk imaging program creates a bit identical copy of a drive which is made by dumping raw data byte by byte, sector by sector from the given disk into an image file. Early disk imaging programs and image formats had a lot of limitations. Because they copied the raw blocks of data from the disk “uninterpreted,” even the unused area or white space was backed up too. This led to very large image files even if the drives or partitions only contained a small amount of data. Copying every sector of a disk in this way worked quite well for “disk cloning,” where everything was being moved to a replacement drive, or was being multi-cast to several computer systems with identical hardware and configurations, but it was not really a very practical solution for regular backup of a system.
Fortunately, disk imaging technologies have been developed that eliminate many of the limitations faced by early adopters of the technology. Most modern disk imaging programs have the ability to interpret the data being copied and remove or compress the empty blocks on a disk which leads to much smaller image files. The majority of programs also create compressed image formats that can be mounted and explored making it possible to retrieve individual files. Also the creation of successive incremental1 or differential2 backups is often supported, which further reduces the demands on storage. Other techniques have been developed that allow file-level operations such as file type filtering, such as the ability to exclude the large and non-essential pagefile.sys and hiberfil.sys from the image, and the ability to image a drive or partition while it is currently in use.
New technologies aside, imaging programs generally still have the ability to do the “old-fashioned” low-level raw copies of a disk which has its advantages. Full bit identical images retain deleted files or lost partitions that have not yet been over-written. All file, file-system, and partition attributes are preserved. Bit identical images facilitate the ability to restore files and partitions to the exact same sectors as the originals. This can prevent such problems as partition misalignment which can cause problems for certain operating systems.3 Since these tools can still handle un-decipherable raw data they can be used to backup any disk even if contains a foreign file system, an unknown operating system, or an encrypted partition.
Advantages of Image Backup Systems
- Allows for rapid full system restores including the operating system on the same or very similar hardware.
- Speed and simplicity is unsurpassed when working with large numbers of files.
- Many modern image formats can be mounted and used like any other drive making accessing backed up files very user friendly.
- Performing image backups is generally much less resource intensive that file backups.
See also: Best Free Drive Cloning Software
File Based Data Backup
File based backup is the type of backup that most people are familiar with. Because this form of backup has been around for so long, the technologies employed are quite numerous, and backup solutions have been developed for about every situation that can be imagined. While only a few dozen different disk imaging programs are currently on the market, literally hundreds, pehaps thousands, of various file backup programs and systems exist.
The simplest form of file based data backup is the basic copy of files from one location to another, but today’s backup programs do a lot more than just simply copying files. File backup programs are designed to automate the process of duplicating files in multiple locations and on numerous types of storage media, locally or across networks or even to remote severs such as online storage. Most have the ability to add files to compressed volumes called archives and at the same time can apply encryption for added security. After performing a full backup of selected data, most backup programs can perform cumulative backups of new or changed files. Popular cumulative backup technologies are incremental1, differential2, delta style4, and binary patching5. Some specialized file backup systems provide continuous (real-time) data protection (i.e., immediately backup up a file as soon as it is created), and others provide versioning systems that will make a new copy of a file each time it is changed. This allows the user to go back and retrieve a previous edition of the file.
The power of file based backup lies in its flexibility. Individuals who are new to backup software are often easily overwhelmed by more advanced programs because of the sheer number of functions and options that these tools may have. Good file backup software can easily be set up to backup certain file types to specific locations using file include and exclude filters. An example of this would be the ability to create a backup “job” that would copy only your digital pictures in .jpeg format to a specific external hard drive, and place them in folders by backup date. At the same time another job could be setup to automatically backup all of your .doc files to online storage where they are safe and can be accessed from another computer. A third job could be configured to find all the files which are larger than a certain size and send them to a compressed archive while the originals are removed to free up space.
Advantages of File Base Data Backups
- Fine control over every aspect of your backup routine.
- Ability to work with small sets of files which is not usually possible with image backups.6
- File fragmentation is greatly reduced if not nearly eliminated in backup archives.
- Easier to restore full backups or migrate data to new or different hardware.
- Generally more practical for remote backups over a network or Internet. (Note: Some new block level copy technologies are helping image based backups to gain some ground in this area as well)
- Real-time backup or continuous data protection and versioning.
- Deduplication technologies work better on file based systems.
- Considered by many to be more resilient to error or corruption than imaging technologies.
See also: Best Free File-Based Backup Program
File Synchronization (“file sync”) is really a specialized adaptation of file based backup technologies. Some would even say it is not true backup, but the result is basically the same. The primary design of sync programs are to replicate or mirror working files in two or more locations where both sets of files will still be put into service. One way to understand the difference between synchronization and backup is that backup copies files in one direction while synchronization copies files (or changes) in two directions. In backup you have a “source” and a “destination.” In true synchronization you really have two sources. For example, when a group of files are set to be synchronized between two computers, files which are changed on any one of the computers will be reflected on the other.
Sync programs also differ from backup programs in that they generally provide detailed control over how file differences or collisions are handled. Files that are renamed, moved or deleted in one location may be renamed, moved or deleted in the other based upon the users choice. This is usually called the ability to “propagate” renames or deletions. Often such programs keep track of files and file operations by creating a database. Among other things the database helps the program differentiate between newly created files and old files that only exist in one location, because they have been deleted in the other.
Synchronization that replicates changes in both locations is called two-way synchronization. Synchronization that only replicates the changes from one location to the second is called one-way synchronization. One-way sync differs from backup when propagate of deletions or renames is performed. Backups do not generally delete files, and a renamed file is usually copied again.
Some people use one-way sync as a way to both backup and synchronize computers. A one-way sync may be made to a portable hard drive. Basically the hard drive becomes a backup destination. The hard drive may then be used as a source to sync with another computer and new files will be transferred from the portable drive to the pc. New files on the second pc may also be backed up to the drive and later to be transferred to the first pc. Thus both computers will remain in sync, and the data on the drive will remain as a backup of both. Similar setups are often used by online storage services which may be looked at as being both online backup as well as online synchronization sources. While Sync programs may provide some sort of data encryption to securely transmit files between locations, they don’t provide compression and packing of files into archives like backup programs.
It is worth noting that many hybrid backup and sync programs to a certain extent perform both file archiving and synchronization.
Advantages of File Synchronization
- Improves productivity when working with the same set of files in different locations.
- Files synchronized to online sources can often be easily accessed from any computer or mobile device such as a smart phone.
- Some programs combine real-time sync with a versioning system that allows for easy collaboration between individuals working on the same file, and usually provide diff comparisons and merging capabilities.
See also: Best Free Folder Synchronization Utility
1. See: “Incremental Backups Explained,. “ for more information on this type of backup.
2. See: “Differential Backups Explained,” for more information on this type of backup.
3. Vista was sometimes left unbootable, some disks take a performance hit, and life span of certain solid state drives (SSD) may be shortened.
4. See: “Delta Backups Explained,” for more information on this type of backup.
5. See: “Binary Patch Backups Explained,” for more information on this type of backup.
6. Some technologies exist to make an image of a single folder but they are not widely implemented.