Aspera Sync FAQ

What does Aspera Sync actually do?

Aspera Sync synchronizes new and modified files and directories between remote endpoints. It moves, deletes, renames, and transfers new file contents as needed. For example:

For additional details on Aspera Sync's core features, see the Introduction.

How does Aspera Sync differ from rsync?

Aspera Sync is a high-speed replacement for rsync in uni-directional mode, and is designed to be a drop-in replacement with similar command-line options (async Command-Line Options). Aspera Sync also supports bi-directional and multi-directional synchronization. The following key capabilities distinguish it from rsync:

To view an example of async options versus rsync options, see rsync vs. async Uni-directional Example.

How is one-time mode different from continuous mode?

As described in Synchronization and Direction Modes, Aspera Sync offers two modes of operation: one-time ("on-demand") synchronization and continuous synchronization. When running in one-time mode, it synchronizes once and exits. In continuous mode, on the other hand, it offers constant synchronization between file systems.

Continuous mode can only be used where file system change notification (that is, inotify, which monitors file system events) is available on the systems that are running async. NFS-mounted file systems do not support inotify change notification for updates made by remote NFS clients, so in these scenarios, async should be run in one-time mode (which can be scheduled through cron). The Sync scan mode is designed for maximum speed and is fully pipelined with transfer, so as to allow for maximum performance even in one-time mode.

In what directions does Aspera Sync work?

Sync works in multiple directions: push, pull, and bi-directional. For more information about Sync direction modes, see Synchronization and Direction Modes.

How are conflicts handled in bi-directional mode?

A conflict situation can arise in bi-directional mode when a file or directory changes content, an entity is renamed before synchronization has completed, or the change occurs on both endpoints concurrently such that the "newer" version cannot be reliably determined. Aspera Sync reports such conflicts and does not modify either file system, leaving the file systems in conflict. For instructions on resolving conflicts, see Resolving Bidirectional Sync File Conflicts.

How much space is required for an Aspera Sync snapshot?

Snapshots require up to 1 GB of disk space for every 1 million files, and an additional 1 GB for cleanup purposes. For optimum performance, Aspera recommends that the file system have at least 2 GB free per 1 million files, and 3 GB free per 1 million files on Windows (due to the poor performance of Windows NTFS when more than half of the available disk space is occupied).