There r two ways to do the job.
<b>Hardware-Based Replication</b>, in this solution it utilizes inherent replication of direct attached storage or SAN to replicate the virtual disk images offsite to another storage device for backup. This usually uses a snap-shot type technology. And the other is
<b>Host-Based Replication</b>, is an asynchronous based technology that on virtual host computer & replicates changes to the virtual disks as they occur & then apply on the target servers in the order of the operation they are received.
Remember, Selecting a flexible data backup and recovery solution helps to provide high availability and also help data center managers better maintain these systems by having the ability to provision, convert and move the systems near or far.
Moreover, u can also use VRanger PRO which is used for backing up virtual machines and their data at the data center or SANMELODY software, which is also used as a SAN Storage Array, and offers asynchronous Replication to mirror the backups.
Hope this may help u !