The H700 is a supported controller on the R310, but you would have to do a clean install or backup/restore. The H310 is also supported on the R310.  It is a low-end hardware RAID controller and would also require a reinstall/restore. The S100 might handle a direct migration of disks from the S300, but as you read, it is not supported under 2012 either.  You can move the disks to the onboard SATA and get rid of the S300, but it would also require a clean install/restore.  If you did the onboard SATA (in AHCI/non-RAID), there would be no RAID managed by the system, but you could set up RAID in Windows, which would provide at least some redundancy.  Performance would not be worse than the S-series controllers. My advice?  Never skimp on storage, no matter what it is being used for.  Always get the top controller (H7x0) when configuring a server.
I would like to upgrade a PowerEdge R310 server from Windows Server 2008 R2 to 2012 R2. Unfortunately the PERC S300 is not supported and I could not find the necessary drivers. I found that the PERC H700 has the right drivers and is compatible with the R310, can anyone confirm that please? Are there cheaper alternatives? Otherwise I think I have to disconnect the PERC controller and connect the disks to the internal SATA ports, but then I would have 4 independent disks with no RAID whatsoever since the embedded PERC S100 is not supported as well... (is there a SW raid solution?) Thanks
Replacing PERC S300 adapter