We have a SAN, with a lun0 which esxi hosts connect to on ISCSI

We want to convert this raid 5 to a raid 6 and increase the size, can this be done without losing data?

Also, i would like to backup our data first, i have two open-e dssv6 SANs. How do i best backup the data to the other SAN? We would like to use synchronous replication, but since the first datastore is going to increase in size and synchrounous replication demands same size, how do we do this the best way if this is the best solution?

Thanks a lot for any answers, hope you can help.