Are you upgrading a NAS Logical Volume to a iSCSI Logical Volume, if so this is not possible to convert these Logical Volumes other than to recreate them. From the post I thought you were asking if you can upgrade a NAS-R3 or iSCSI-R3 product to DSS without losing the data.
Yes , please make backup first. If you have another system you can use the Demo-CD to replicate data by using the Data Replication feature so you will have another copy.