Hidden in the back pockets of a few savvy system administrators is a free, mature, and open source file synchronization tool called Unison. Like sound coming together from two speakers, Unison does a solid job synchronizing smaller files and directories between (at most) 2 systems. <\/p>\n\n\n\n
Unison provides bidirectional (two-way) file synchronization software. What\u2019s different from other file synchronization tools like Rsync is that Unison is truly bidirectional: Users may create or change files and directories on either system. In Unison vernacular, each system is known as a replica. Unison also tracks file changes. In situations where Unison detects a conflict (e.g., when two users are updating the same file) it must be resolved manually. <\/p>\n\n\n\n
Unison also works in client-server, hub-and-spoke topology for backup & sync. Each spoke pairs with the hub; thus, changes are only propagated between the hub and the one spoke. This is by no means real-time nor scalable, but may suffice for basic file backup use cases. <\/p>\n\n\n\n
Unison runs on a variety of Unix-like operating systems (Linux, macOS\/macOS X, Solaris, FreeBSD, et al) and Microsoft Windows. You can install a graphical user interface or drive Unison from the command line. Unison is cross platform and you can backup & sync files between different operating systems (e.g. from Unix to Windows) but according to the Unison Readme each system must include an OCaml compiler. The Unison FAQ<\/a> recommends keeping the same software versions on all replicas. <\/p>\n\n\n\n Unison is a bit like a bidirectional version of Rsync that handles some level of version control. The big difference between Unison and Rsync is that Rsync is only unidirectional\u2014i.e., syncs files one-way, from a source to a target system. Practically speaking, both Rsync and Unison were designed in the 90\u2019s\u2014Unison being released in 1998\u2014when file sizes and file systems were much smaller, and there were fewer numbers of files. In modern implementations, as the number of files grows, or file sizes increase, Unison may bog down. Like Rsync (and other free tools like DirSync Pro to Synctoy), Unison also relies on scanning the file system and reading all files into memory to build an index of which files have changed. <\/p>\n\n\n\n Unison\u2019s major limitations are primarily architectural: each of the 2 Unison systems are points of failure. And Unison file synchronization jobs don\u2019t scale beyond the 2 systems. There are the caveats mentioned earlier around file sizes, number of files, network conditions, and so forth. Another limitation is that changes to files may not always be captured and replicated. <\/p>\n\n\n\n Without the ability to capture file changes in real-time, Unison (as well as rsync and other point-to-point tools) are not practical solutions for systems containing larger numbers of files. That said, the Unison file synchronizer may be useful in scenarios such as: <\/p>\n\n\n\n In these scenarios above, you might also consider Resilio Sync for basic two-way file synchronization or \u201cfreefilesync\u201d. <\/p>\n\n\n\n As a Unison file sync alternative, consider using Resilio Platform for scenarios such as: <\/p>\n\n\n\n For larger customers or users with more extreme scale data movement requirements, some challenges with Unison and other conventional point-to-point file sync tools may include: <\/p>\n\n\n\n Large files not supported<\/strong>: Unison may not be able to transfer or sync files, leading to “lost connection to the server” and other errors. Resilio Platform has no limits on file sizes or types. <\/p>\n\n\n\n No real-time file change detection<\/strong>: Unison, Rsync, and other conventional folder comparison and file synchronization tools are not real-time. Unison could theoretically be configured to track iNotify file system notifications in Linux but Unison is not real-time nor file-change-aware out of the box. By contrast, Resilio Platform offers highly efficient, real-time file change replication for a variety of operating systems (Windows, Linux, et al) to detect and replicate changes on-the-fly in real-time.<\/p>\n\n\n\n Poor file system scalability<\/strong>: As file sizes and file system sizes grow into the many thousands to millions of files, Unison may bog down and reach its limits. Unison\u2019s architecture is limited by resources within two systems (replicas) such as memory, CPU, and storage IO\u2014as well as the indexing architecture. Larger files and larger numbers of files may not synchronize; or be limited by the time it takes to index a file system or directory, find, coalesce, and propagate changes to the replica. <\/p>\n\n\n\n WAN connections problematic<\/strong>: Unison is not WAN optimized. Wide-area networks (WANs) or\u00a0 unreliable networks (such as Cell, VSAT, et al) may incur latency and long retransmission times and varying degrees of packet loss which will degrade Unison\u2019s transfer and file sync performance, or cause failures.\u00a0 By contrast, Resilio Platform includes WAN optimization. With Active Everywhere you can utilize 100% of the available bandwidth in your network independent of distance, latency, or loss. You can read more about Resilio WAN optimization here<\/a>.<\/p>\n\n\n\n Sheer scalability limitations<\/strong>: In the Unison model, the synchronization job will always be limited to 2 replicas. While Unison supports a hub-and-spoke topology, files can not be concurrently synchronized to multiple replicas. Thus, a common approach with rsync and other basic sync tools is to \u201cfollow the sun\u201d, executing jobs individually; once the previous job completes, a second job is started, and so forth. What was reasonably quick for one-to-one transfers becomes very slow when it has to be repeated many times, serialized in sequence. <\/p>\n\n\n\n By contrast, Resilio Platform uses a distributed, peer-to-peer approach that leverages networking between all offices\/servers and significantly speeds up data transfers<\/a>. Resilio\u2019s optimized approach dramatically speeds up syncing operations: Resilio transfers concurrently to N-number of destinations. Resilio also makes efficient use of all the available network capacity that may otherwise be left unused.<\/p>\n\n\n\n Problems with firewalls, NATs, DHCP<\/strong>: Unison includes some basic networking capabilities. Resilio Platform makes it incredibly easy to deal with firewalls, NAT, and DHCP. Resilio Platform also includes a Proxy Server<\/a> to simplify the configuration for remote users and systems administrators needing the flexibility to traverse a variety of home networks, remote offices, and on-prem firewalls and DMZs.<\/p>\n\n\n\n Data protection and encryption<\/strong>: While Unison supports SSH and using VPNs, the product lacks native encryption for files at rest and in transit. Resilio Platform protects and encrypts files at rest and in flight. Resilio uses AES256 in CTR mode to encrypt all the traffic sent between endpoints.<\/p>\n\n\n\n Through real-time file synchronization and other key capabilities, Resilio Active Everywhere<\/a> accelerates file delivery concurrently across any network, up to 10x faster than Unison and other conventional file sync software. Resilio enables true multi-directional (N-way) file synchronization to overcome file sharing and transfer bottlenecks over WANs.\u00a0<\/p>\n\n\n\n Architecturally, Resilio Platform is an agent-based solution.\u00a0 Resilio Agents <\/em>are installed on all devices participating in data movement jobs<\/em>.\u00a0 Job types include Distribution, Consolidation, Scripting, and Synchronization. Resilio Platform agents support popular operating systems such as Windows, Mac, Linux, FreeBSD, and Android.\u00a0 Active Everywhere also supports popular virtualization platforms, servers, storage, NAS devices, networks, and cloud providers.\u00a0\u00a0<\/p>\n\n\n\n The Resilio Platform Management Console<\/em> is a centralized, web-based management system used to manage and monitor all job functions through an easy-to-administer graphical user interface. Optionally, Resilio offers a complete API set to expose and automate all functions performed by the Management Console. The Management Console may be installed on Windows and Linux servers. <\/p>\n\n\n\n Here is a handy summary table of the features needed in a synchronization solution today, and how Resilio Platform stacks up as a solid Unison file sync alternative.<\/p>\n\n\n\n <\/p>\n\n\n\n\n
Unison Alternatives:\u00a0 When to consider Resilio Active Everywhere<\/h2>\n\n\n\n
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Technical considerations in a Unison file sync alternative <\/h2>\n\n\n\n
A Modern Unison File Sync Alternative<\/strong>: Resilio Active Everywhere<\/h2>\n\n\n\n
Resilio Active Everywhere vs. Unison – Feature Comparison<\/h1>\n\n\n\n