MegaRAID Storage Manager Error 1920 “Service MRMonitor (MegaMonitorSrv) failed to start.” on Windows Server 2003 R2 x64

First off all, see this post: What are the different widely used RAID levels and when should I consider them

Notice the difference between RAID 10 and RAID 01.

Match this to your setups (both of them labeled as RAID 10 in your text). Look carefully.

Read the part in the link I posted where it states:
RAID 01 Good when: never Bad when: always

I think your choice should be obvious after this.

Edit: Stating things explicitly:

Your first setup is a mirrored pair of 4 drive stripes.

  Span 0:  4 drives in RAID0  \
                               }  Mirror from span 0 and span 1
  Span 1:  4 drives in RAID0  /

If any drives fails in a stripe then that stripe of lost.
In your case this means:

1 drive lost -> Working in degraded mode.

2 drives lost. Now we use some math.
If the drive fails in the the same span/stripe then you have the same result as 1 drive lost. Still degraded. One of the spans is off-line

If the second drive happens in the other span/stripe: Whole array off line. Consider your backups. (You did make and test those, right?)

The chance that a second drive fails in the wrong span is 4/7^th (4 drives left in the working span, each of which can fail) and only 3/7^th that is fails in the span which is already down. Those are not good odds.

Now the other setup, with a stripe of 4 mirrors.

1 drive lost (any of the 4 spans): Array still works.

2 drives lost: 85% chance that the array is still working. That is a lot better then in the previous case (which was 4/7th, or 57%).

TL:DR: use the second configuration: It is more robust.

This problem of drivers not recognised (in my case it was megaraid sas 8708em2) when building 2012R2 off USB stick is really wacky. Wasted a good part of my day, looking for LSI (now Broadcom) drivers, finding them (Windows 8.1 apparently works for 2012R2) but not having any success. USB install I can confirm does not work for this particular LSi raid. So I configured the server to boot from pxe option and enabled 2012R2 build image on my WDS server. Pressed F12 and was able to install the same OS I had on USB stick, this time no problems with missing drivers. What is it that makes installation of 2012R2 possible using pxe method, and impossible using USB method (identical ISO media used), I do not know. I do not even have "X19-03239" ISO, the version is different but the solution is to use pxe method instead. Hope this helps, albeit 3 years down the line.