centranex

You need to enter the controller's (HBA's) Array Configuration Utility and simply setup the disks as JBOD. It was functioning flawlessly with DSM 5.2

I actually noticed that it appears to be functioning but it is giving errors like: synoscgi_SYNO.Storage.CGI.Storage_1_load_info[31452]: disk/disk_exceed_unc_thr_cache.c:28 Failed to get exceed unc thr from /run/synostorage/disks//sdc/exc_bad_sec_ct synoscgi_SYNO.Storage.CGI.Storage_1_load_info[31452]: disk/disk_is_below_life_thr_cache.c:28 Failed to get below remain life thr from /run/synostorage/disks//sdc/below_remain_life_thr I also installed 4 new disks and unable to create a Raid-5 disk group, it fails.

I can confirm that by using the extra custom ram disk created by @IG-88, I was able to migrate from DSM 5.2 to 6.1.3 with the Adaptec 6405E controller. The only thing that broke for me was all of my iSCSI targets, but I attempted to create a brand new iSCSI LUN + Target and it came online. I will continue to investigate, but I doubt that it has anything to do with the missing driver at first.