You will need to backup and restore for this one.  Configuring RAID will destroy the data on the existing disk.  Because the H310 supports non-RAID, you "might" be able to put both disks on the H310 in non-RAID mode, but performance wise, you'd be probably better off with them attached to the motherboard in a Windows-managed RAID 1/mirror. Backup, add disks to H310, configure RAID, restore (this would need to be a file-level backup/restore, or your backup utility would need to support restoring to a different controller, capable of adding the driver in the process).
Greeting all,   I am now using no raid , no controller, 1 HDD. (non hotplug) running on windows small business 2011 Essentials. Recently I purchased a H310 raid card + 1 identical HDD (non hotplug) to do a Raid 1 configuration.   Before installing these 2 components, what do I need to prepare/do before taking down Server? Also, Anyone could link me a guide to installation ? (Before, install, and after )   Thanks! 
Steps for install Raid 1 H310 card + additional HDD on T320 server? 