Im still looking around for information but some have caught my eye and might help you too @Tonny.
It seems that the controller PERC H730 Mini is perfectly ready for SAS-3 (12) BUT I have two SAS drives ST600MM0006 (RAID1) and four SAS drives ST2000NM0023 (RAID5) and they seem to go only up to SAS-2 (6). It could be that the controller itself then falls back everything to SAS-2. The iDRAC tells me that all drives are just hitting SAS-2 while it reports that the controller itself can hit SAS-3.
BTW, after enabling that "Read Ahead" Im hitting this:
Intrestingly, I changed to passthrough and Im getting slightly worst performance then after enabling "Read Ahead":
My last test would be passthrough on SCSI controller. It is on a IDE controller because RemoteFX isnt compatible.
Sadly I cannot get it to boot off a passthough SSD attached to a SCSI controller in Windows Server 2012 R2's Hyper-V. Limitation?
Well the best I can do is boot off a VHDX on a IDE controller and passthrough the SSD to a SCSI controller. These are the results:
Intresting results. Write speeds improve and read speeds SLIGHTLY go down.
I directly attached the SSD to the Hyper-V host and then ran CrystalDiskMark on the actual Hyper-V host (no virtualization)
Speeds are not that impressive so I would tend to start to believe that the issue is the controller (or its driver).