How do you choose between file- and block-level replication?

Block-level and file-level replication are both designed to copy data from one storage location to another. Block-level replication copies individual storage blocks, whereas file-level replication copies entire files rather than the blocks that make up those files.

Block-level replication is probably best suited for backup applications. The reason is that block-level replication makes it easy to perform incremental or differential backups. If a small modification is made to a file, it is possible to back up only the storage blocks that have been modified rather than the entire file. If, for example, a 1 KB change was made to a 10 GB file, it would be much more efficient to back up the 1 KB that had been modified instead of copying the entire file.

Block-level replication is also useful for situations in which file versioning is required. As changes are made to a file, the replication mechanism can keep track of the blocks that have been modified and allow users to revert to a previous version of a file without performing a traditional restoration.

In contrast, file-level replication is best suited to file sync-and-share applications. Imagine for a moment that a particular user needed to work offline. Replicating the files from a network share to the user's laptop ensures the user has the necessary data before going offline. If the user creates or modifies any files while working offline, those files can be synchronized to the network the next time the user connects. In addition, any new files that were created on the network while the user was offline are replicated to the user's laptop the next time they connect.