Christopher (Drashna)

I assume you have no duplication. I would, provided I have enough ports:
Physically remove the faulty HDD (you have done this already) Remove it through the DP UI -> This should stop DP complaining about a missing disk and unlock the Pool. Add the two new HDD to the Pool Remove the two old HDDs from the Pool through the UI -> This will move all files to the new HDDs Remove the two old HDDs physically from the Server Then see what you can recover from the faulty HDD and copy that back to the Pool. I would consider to keep the two performing old HDDs in the Pool and use x2 duplication.

Yup.  It's a lifetime license that belongs to you, and includes all upgrades, and can be moved to a new system/OS.
I'm glad to hear it! 
And yeah, the automatic rebuild of the pool is very nice!

So, removing StableBit Scanner from the system fixed the issue with the drives? 
If so.... well, uninstalling the drivers for the controller (or installing them, if they weren't) may help out here. 
Otherwise, it depends on your budget.  I personally highly recommend the LSI SAS 9211 or 9207 cards, but they're on the higher end of consumer/prosumer. 

Thanks for your reply I appreciate it, I was expecting that answer but its always best to ask.
I really like the idea of clouddrive and drivepool working together with my drobo and google apps, it will be worth the effort I think.

Yup, we use volume IDs to track the disks, actually.
However, there is some changes to how that's handled in the latest beta, so this may not be an issue in the future. 

Thanks - I'll set this all up once I can get my hands on a good sized SSD drive to use as my cache for the clouddrive.

Actually, yes.  That's part of what we want to do with StableBit Cloud.
Good news!  the latest beta has a concurrency limit, that you can configure.  It defaults to 2 drives, right now.  So this should help you out greatly! 
http://dl.covecube.com/CloudDriveWindows/beta/download/StableBit.CloudDrive_1.1.1.1057_x64_BETA.exe
 

I think I found where my issue was occurring, I am being bottle necked by the windows OS cache because I am running the OS off a SATA SSD. I need to move that over to part of the 970 EVO. I am going to attempt that OS reinstall move later and test again.
Now the problem makes a lot more sense and is why the speeds looked great in benchmarks but did not manifest in real world file transfers.

Yeah, the pooled drives have hidden "PoolPart" folders on each drive. Along with some super hidden data that ID's the pool.  And duplication settings are stored the same way. 
But glad to hear that migration was dead simple! 

Well, for moving the pool over to new drives, you could just copy from one pool to another.  No need to share the poolpart folders.  In fact.... by doing that, you may end up making more work for yourself. (eg, duplication)

Jaga, Christopher,
 
Thank you, migration was very easy indeed, StableBit software picked pools up without any issues, these pools must have all required metadata inside I believe.
 

To be blunt, when talking about storage, it's a good idea to take things with a grain of salt.  There are a lot of misconceptions and myths that get perpetuated, even by smart and experienced people. 
Worse, is that some things may have been true at one point, but technology and the like improved, but people still believe what once held true.
That said, StableBit Scanner polls SMART data once a minute, by default.  And you can configure that interval, if you want.
As for the stuff mentioned, unless you have a bad drive (either failing, or poorly designed), I don't think that this is actually an issue on modern drives, and the issues mentioned are an exaggeration. 

I used this adapter cable for years & never had a problem. Before I bought my server case I had a regular old case. I had (3) 4 in 3 hot swap cages next to the server. I ran the sata cables out the back of my old case. I had a power supply sitting on the shelf by the cages which powered them.
The cool thing was that I ran the power cables that usually go to the motherboard inside of the case from the second power supply. I had a adapter that would plug into the motherboard and the main power supply that the computer would plug into. The adapter had a couple of wires coming from it to a female connection. You would plug your second power supply into it. 
What would happen is that when you turn on your main computer the second power supply would come on. That way your computer will see all of your hard drives at once. Of course when you turned off your server both of the power supplies would turn off.
Here is a link to that adapter. Let me know what you think.
https://www.newegg.com/Product/Product.aspx?Item=9SIA85V3DG9612

This is what it's supposed to do: 

 
But if it's working now, then that's fine.

Nope, different protocol.  But trust me when I say that NVMe health is FAR superior to SMART. 
Awesome. 
As for protocol: 
http://blog.covecube.com/2018/05/stablebit-scanner-2-5-2-3175-beta/
That has a picture of it. 

The current method of separate modules, where we can pick and choose which options to use together gets my (very strong) vote!
Jamming them all together will just create unneeded bloat for some.
I would still pay a "forced" bundle price, if it gave me the option to use just the modules I need... and maybe add one or more of the others later.
I'm amazed at the quality of product/s that one (I think?) developer has produced and offering for a low - as Chris says, almost impulse buy - price.
Keep up the good work and bug squashing guys!

It's just exaggerated. The URE avg rates at 10^14/15 are taken literally in those articles while in reality most drives can survive a LOT longer. It's also implied that an URE will kill a resilver/rebuild without exception. That's only partly true as e.g. some HW controllers and older SW have a very small tolerance for it. Modern and updated RAID algorithms can continue a rebuild with that particular area reported as a reallocated area to the upper FS IIRC and you'll likely just get a pre-fail SMART attribute status as if you had experienced the same thing on a single drive that will act slower and hang on that area in much the samme manner as a rebuild will. 
I'd still take striped mirrors for max performance and reliability and parity only where max storage vs cost is important, albeit in small arrays striped together.

To clarify a couple of things here (sorry, I did skim here):
StableBit DrivePool's default file placement strategy is to place new files on the disks with the most available free space.  This means the 1TB drives, first, and then once they're full enough, on the 500GB drive.    So, yes, this is normal.
The Drive Space Equalizer doesn't change this, but just causes it to rebalance "after the fact" so that it's equal.  
So, once the 1TB drives get to be about 470GB free/used, it should then start using the 500GB drive as well. 
 
There are a couple of balancers that do change this behavior, but you'll see "real time placement limiters" on the disks, when this happens (red arrows, specifically).  If you don't see that, then it defaults to the "normal" behavior. 

To clarify a couple of things here (sorry, I did skim here):
StableBit DrivePool's default file placement strategy is to place new files on the disks with the most available free space.  This means the 1TB drives, first, and then once they're full enough, on the 500GB drive.    So, yes, this is normal.
The Drive Space Equalizer doesn't change this, but just causes it to rebalance "after the fact" so that it's equal.  
So, once the 1TB drives get to be about 470GB free/used, it should then start using the 500GB drive as well. 
 
There are a couple of balancers that do change this behavior, but you'll see "real time placement limiters" on the disks, when this happens (red arrows, specifically).  If you don't see that, then it defaults to the "normal" behavior. 

No.  Missing disks cause the pool to go read only. Period. 
There has never been an option to change that, because any data written could cause corruption, as the data may/will get out of sync.   So to prevent that, the pool is made read only until the missing disk is resolved. 

RIP Essentials.  Rip WHS. 
2019 Essentials is a rebrand of the "Foundation" server SKU.  
It lacks everything that makes Essentials "Essentials".  That means no: 
Dashboard Connector Client Backup and Restore Remote Access website (aka Anywhere Access) Office 365 integration etc What it does give you?  A neutered version of Standard, without the need for CAL (client Access Licenses).  Which is a joke/slap in the face to the Home Server community.  (This is my personal opinion and not representative of Covecube)
 
If you want the WHS experience, ... that's not Server 2019, at all.  
If you want a cheap(er) server OS but don't want to deal with all the licensing involved with servers and are okay with some key features being removed/not present, then 2019 Essentials should be "good enough"
Mainstream support (til 2022) gets updates to the "Essentials" code, and "new features".  After that, and until 2027, it is only security patches. No feature fixes, no new features, etc. 
 
Yeah, the folder structure is because it's a domain controller (the sysvol and netlogon shares).  These are non-negotiable for Essentials.  The File History and Folder Redirection stuff is optional, but nice.  
That's why you're supposed to use the "Shared Folders" folder on Essentials. It mostly has all the folders that you want, and none of the system stuff. 
And Veeam is a very popular choice. 
You're very welcome!  Paul "Tinkertry" was one of the very active members of the WHS community, and he has a lot of good info on his blog.
My recommendation would be Windows Server 2016 Essentials.   Because with the Standard version, you're supposed to buy User CALs, as well. 
As for flexibility, there are only a couple of things missing from standard. And that's mostly data deduplication, which doesn't work on the pool, actually.  So, you really don't miss out on much. 

Yeah, I think it was depreciated, as we drastically overhauled the removal process, to make it much more seamless.  
In fact, when removing a disk now, the pool is not put into a read only mode.  Though, duplicated data may be "marked" as read only (errors out on writes). So this setting was rendered obsolete. 

Just updating to say that this works extremely well. I've uploaded almost 35 TB in 8 1/2 days with no issues. This is great software. 

Windows Server 2016 Essentials is a very good choice, actually!  It's the direct successor to Windows Home Server, actually.  The caveat here is that it does want to be a domain controller (but that's 100% optional). 
Yeah, the Essentials Experience won't really let you delete the Users folder. There is some hard coded functionality here, which ... is annoying. 
Depending on how you move the folders, "yes".  Eg, it will keep the permissions from the old folder, and not use the ones from the new folder. It's quite annoying, and why some of my automation stuff uses a temp drive and then moves stuff to the pool. 
If you're using the Essentials stuff, you should be good.  
But you should check out this: https://tinkertry.com/ws2012e-connector
https://tinkertry.com/how-to-make-windows-server-2012-r2-essentials-client-connector-install-behave-just-like-windows-home-server
 

Windows Server 2016 Essentials is a very good choice, actually!  It's the direct successor to Windows Home Server, actually.  The caveat here is that it does want to be a domain controller (but that's 100% optional). 
Yeah, the Essentials Experience won't really let you delete the Users folder. There is some hard coded functionality here, which ... is annoying. 
Depending on how you move the folders, "yes".  Eg, it will keep the permissions from the old folder, and not use the ones from the new folder. It's quite annoying, and why some of my automation stuff uses a temp drive and then moves stuff to the pool. 
If you're using the Essentials stuff, you should be good.  
But you should check out this: https://tinkertry.com/ws2012e-connector
https://tinkertry.com/how-to-make-windows-server-2012-r2-essentials-client-connector-install-behave-just-like-windows-home-server