Well, with StableBit CloudDrive, I can understand that. The caching we do may cause issues with their internal caching algorithms.
But for DrivePool to have performance issues with them is very odd.
Before returning them, I'd like to see if we can troubleshoot a bit first. That way, you don't have to go through the trouble of returning the drives.
Specifically, try installing this version:
There are a whole bunch of bug fixes and performance tweaks that may solve the problem outright (with the pool at least).
If that doesn't help, enable file system logging, and reproduce the issue. Upload the logs once you've done that.
Also, run this:
Microsoft MVP for Windows Home Server 2009-2012
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Lots of "Other" data on your pool? Read about what it is here.