There are different reasons why your system may be slow to boot from your Intel® SSD DC P3700 sometimes.
First, I would like to mention that Intel PCIe SSD's with NVMe technology have different requirements, however, some systems that meet the basic requirements may require additional steps to make full use of these drives. We advise you to check with Asus about the optimal settings required in the BIOS for your system to boot from a PCIe* NVMe* SSD.
The documents we have do not include motherboards with C612 chipsets, however, you might want to review them and use for reference:
You may also check the following items, as they have helped other users to improve boot times in their systems:
1. Contact the Computer Manufacturer Support to obtain and update the BIOS of your motherboard BIOS. This may improve support for NVMe devices.
2. Update the Firmware of your Intel® SSD DC P3700 using Intel® SSD Data Center Tool (currently 2.3.1)
3. Make sure to use the current version of the Intel® Solid-State Drive Data Center Family for NVMe Drivers (currently 220.127.116.117).
4. Confirm that the SSD is connected to a PCIe Gen 3.0 x4 Slot, or try using a different PCIe slot.
The SSD should be operating properly after applying the actions mentioned previously. Please take into consideration that the Intel® SSD DC P3700 Series is designed to deliver performance, reliability and endurance for Data Center systems that require hardware and data integrity to be fully checked when the system is initialized, also, Data Center systems often remain on for long periods.
We are continuously working to improve firmware and drivers, however, we do not expect future releases to make any major changes regarding boot times and the initialization process of the Intel® SSD DC P3700's.
If you wish to optimize boot times in your system, we advise you to consider external reasons, such as boot order and disconnecting USB devices or other components that may be causing the overall initialization process to take longer.
When you say that your boot times are "very slow", exactly how long is it taking you to get to the Windows login screen?
I have a somewhat similar setup:
Asus X99 Deluxe
400 GB Intel P3700 PCI-e
64GB Corsair Dominator Platinum
Windows 10 Pro
6 GB AMD 7990 GPU
Raid 5 array with six varies drives
While the system boots fast compared to a "normal" PC, I was expecting it to boot significantly faster. I would estimate that it takes about 15-20 seconds to boot to the Windows login screen.
I have another rig that is using a M.2 drive for the OS and running Win 7 Pro - it boots way faster - probably 6-7 seconds.
Not sure if it is a Windows 10 thing or a drive thing.