TerryMundy

As you mentioned, the simplest method is to physically disconnect the drive or take it offline via Windows Disk Management; both will result in DrivePool noticing the disk is missing, allowing you to Remove it without affecting the files - however if you don't rename or remove the poolpart folder (a "hidden" folder on the drive) before reconnecting/onlining the drive again it may be rejoined to the pool.
To pre-empt that issue, you can either rename the poolpart folder before disconnecting/offlining the drive (though this may not be possible if there are any open file handles*) or you can open a command prompt as an administrator and enter the following command:
dpcmd ignore-poolpart pooldriveletter poolpartfoldername where pooldriveletter is the drive letter (including the colon) of the pool - not the poolpart - and poolpartfoldername is the name of the poolpart folder that is on the drive you wish to remove. This will "tag" the poolpart folder so that DrivePool will immediately disconnect the poolpart and also ignore it in future.
For example: dpcmd ignore-poolpart k: PoolPart.9be9560f-2871-4c99-9722-7269f0250cfa
* the commands dpcmd list-open-files and dpcmd force-close-open-files can be useful for dealing with this.
Just a reminder that if you are using SnapRAID with a pool, generally you should turn off balancing for that pool (to prevent DrivePool moving files between volumes).

Spider99,
Thank you!  I found a few explanations and how to "shade tree mechanic" fix it, but this appears to be the least troublesome and easiest way out.  You are a hero!
When building systems at work cooking up a Nimble Storage Array with 1PB when it's not my money is up my alley.  But building on the cheap at home with garage sale parts required more thought.  Like playing chess it 4D.  It just blows the mind.
Now off to find some chassis to house the 3.5" SATA drives as 16 are 2.5" and work flawlessly in the MSA70.
Maybe I can get out of the dog house once all of the home movies and family photos are back online.
Once again, this forum has saved my bacon and I only hope to become knowledgeable enough to help others as I've been helped.
Much appreciate the quick answer!
Terry