Hard drives choices?

Yes, the concerns about SSD writing endurance have been downgraded to 'old wives' status as the flash arrays have gotten better over time, and write endurance (measured in TBW, terabytes written) for even average consumer-grade drives is encroaching on the petabyte range for 500GB drives.
 
As for speed, I've been noodling around with various combinations of audio drives for my CbB environment. I've used dual SSD in RAID-0, single SSD, dual HDD in RAID-0 and of course single HDD.  The usage experience doesn't change enough at all between those combinations to make me choose one over the other.  As long as the CbB code, plug-ins, and picture cache are on an SSD, the rest (up to about 120 tracks) is a matter of bragging rights. 
 
Now that the Win10 updates have un-broken my mouse and USB interface problems, I'm going to update 4th-article in 4-article series on my website called Homemade Hybrid Disk Drives.  I'm now back to the original intent of a RAM cache backed by an SSD cache.  The benefits in a for video editing are rather obvious.  The benefits for audio tracking/editing/mixing are rather hard to see. 
 
 

Use that M.2 for samples!
A 250gb SSD for OS.
Personally where I see the SSD shine for the OS is the VST scan time when Splat and CbB launch. IMHO, most of the improvement in OS speed is the “clean” install to the SSD.
Other than the VST scan, migrating to SSD in my old Cat was mostly a big yawn; just my personal experience and opinion.
Your sata 3 HD’s for your audio and data will be fine.
Just my nickel 98’s worth.
I wouldn’t “waste” that m.2 on the OS!
It will load your samples almost before you open the project.
You can thank me later.
T

Hmmm. Funny you 2 guys posted because I was now coming back to ask about the heat issue with the nvme m.2. Seems they run really hot. Mine is the Evo 970 500GB.
 
Maybe I will use it for samples as suggested, I do use softsynths and midi all the time.
I do have a new unopened Evo 850 250gb SSD. Perhaps thats a better choice for the OS.
The last few years I have had an Intel 240GB SSD as my os drive and it has 108GB free.
 
The Asus borad de oes have a huge heatsink for one of the m.2  slots. 
 
I know I'll be back with questions...............Thanks so much

That 970 EVO sustains ~3400MB/Sec.
It'll load sample libraries fast... and you'll be able to achieve high disk-streaming polyphony.
 
M.2 Ultra (NVMe) SSDs are perfect for libraries that load a bit slow.
ie: HALion 6 loads a bit slow...
Put the library on a M.2 Ultra SSD... and it's much more snappy.
 

Starise
Isn't some of this dependent on available cpu lanes when using multiple drives?

M.2 Ultra SSDs do require 4 PCIe lanes to operate at full speed.