File synchronization (or syncing) in computing is the process of ensuring that

computer file A computer file is a System resource, resource for recording Data (computing), data on a Computer data storage, computer storage device, primarily identified by its filename. Just as words can be written on paper, so too can data be written to a ...

s in two or more locations are updated via certain rules. In ''one-way file synchronization'', also called

mirroring Mirroring is the behavior in which one person subconsciously imitates the gesture, idiolect, speech pattern, or attitude of another. Mirroring often occurs in social situations, particularly in the company of close friends or family, often going ...

, updated files are copied from a source location to one or more target locations, but no files are copied back to the source location. In ''two-way file synchronization'', updated files are copied in both directions, usually with the purpose of keeping the two locations identical to each other. In this article, the term synchronization refers exclusively to two-way file synchronization. File synchronization is commonly used for home backups on external hard drives or updating for transport on

USB flash drives A flash drive (also thumb drive, memory stick, and pen drive/pendrive) is a data storage device that includes flash memory with an integrated USB interface. A typical USB drive is removable, rewritable, and smaller than an optical disc, and ...

. BitTorrent Sync,

Dropbox Dropbox is a file hosting service operated by the American company Dropbox, Inc., headquartered in San Francisco, California, that offers cloud storage, file synchronization, personal cloud, and Client (computing), client software. Dropbox w ...

, SKYSITE,

Nextcloud Nextcloud is a suite of Client–server model, client-server software for creating and using file hosting services. It can integrate with the Collabora Online and OnlyOffice office suites. It can be hosted in the Cloud computing, cloud or On-pre ...

OneDrive Microsoft OneDrive is a file-hosting service operated by Microsoft. First released as SkyDrive in August 2007, it allows registered users to store, share, back-up and synchronize their files. OneDrive also works as the storage Frontend and backe ...

Google Drive Google Drive is a file-hosting service and synchronization service developed by Google. Launched on April 24, 2012, Google Drive allows users to store files in the cloud (on Google servers), synchronize files across devices, and share files ...

and

iCloud iCloud is the personal cloud service of Apple Inc. Launched on October 12, 2011, iCloud enables users to store and Data synchronization, sync data across devices, including Apple Mail, Calendar (Apple), Apple Calendar, Photos (Apple), Apple Ph ...

are prominent products. Some

backup software In information technology, a backup, or data backup is a copy of computer data taken and stored elsewhere so that it may be used to restore the original after a data loss event. The verb form, referring to the process of doing so, is " back up ...

also support real-time file sync. The automatic process prevents copying already identical files and thus can be faster and save much time versus a manual copy, and is less error prone. However this suffers from the limit that the synchronized files must physically fit in the portable storage device. Synchronization software that only keeps a list of files and the changed files eliminates this problem (e.g. the "snapshot" feature in Beyond Compare or the "package" feature in Synchronize It!). It is especially useful for mobile workers, or others that work on multiple computers. It is possible to synchronize multiple locations by synchronizing them one pair at a time. The

Unison Unison (stylised as UNISON) is a Great Britain, British trade union. Along with Unite the Union, Unite, Unison is one of the two largest trade unions in the United Kingdom, with over 1.2 million members who work predominantly in public servic ...

Manual describes how to do this: : If you need to do this, the most reliable way to set things up is to organize the machines into a "star topology," with one machine designated as the "hub" and the rest as "spokes," and with each spoke machine synchronizing only with the hub. The big advantage of the star topology is that it eliminates the possibility of confusing "spurious conflicts" arising from the fact that a separate archive is maintained by

for every pair of hosts that it synchronizes.

Common features

Common features of file synchronization systems include: *

Encryption In Cryptography law, cryptography, encryption (more specifically, Code, encoding) is the process of transforming information in a way that, ideally, only authorized parties can decode. This process converts the original representation of the inf ...

for

security Security is protection from, or resilience against, potential harm (or other unwanted coercion). Beneficiaries (technically referents) of security may be persons and social groups, objects and institutions, ecosystems, or any other entity or ...

, especially when synchronizing across the

Internet The Internet (or internet) is the Global network, global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a internetworking, network of networks ...

. * Compressing any data sent across a network. * ''Conflict detection'' where a file has been modified on both sources, as opposed to where it has only been modified on one. Undetected conflicts can lead to overwriting copies of the file with the most recent version, causing data loss. For conflict detection, the synchronization software needs to keep a database of the synchronized files. Distributed conflict detection can be achieved by version vectors. * ''Open Files Support'' ensures data integrity when copying data or application files that are in-use or database files that are exclusively locked. * Specific support for using an intermediate storage device, such as a removable flash disc, to synchronize two machines. Most synchronizing programs can be used in this way, but providing specific support for this can reduce the amount of data stored on a device. * The ability to preview any changes before they are made. * The ability to view differences in individual files. * Backup between operating systems and transfer between network computers. * Ability to edit or use files on multiple computers or operating systems.

Comparison to shared file access

Possible security concerns

Consumer-grade file synchronization solutions are popular, however for business use, they create a concern of allowing corporate information to sprawl to unmanaged devices and cloud services which are uncontrolled by the organization. When using cloud services, data privacy risks can be mitigated by using a file synchronization solution that features

end-to-end encryption End-to-end encryption (E2EE) is a method of implementing a secure communication system where only communicating users can participate. No one else, including the system provider, telecom providers, Internet providers or malicious actors, can ...

instead of simple transport (

HTTPS Hypertext Transfer Protocol Secure (HTTPS) is an extension of the Hypertext Transfer Protocol (HTTP). It uses encryption for secure communication over a computer network, and is widely used on the Internet. In HTTPS, the communication protoc ...

) or at-rest encryption.

References

{{DEFAULTSORT:File synchronization Storage software Utility software types

Common features

Comparison to shared file access

Possible security concerns

See also

References