Replicating storage efficiently

On the block level, the synchronization can be done using Starwind that makes a mirrored disk on both ends. It can run over iSCSI LUNs, making active-active storage. No additional hardware required.

On the file level, lsyncd and rsync do a mirror synchronizing files between servers. These tools might require tweaking the configuration files in order to ensure the file locking mechanism works as expected and no split-brain would occur.