drivepool_user

Mirror using virtual hard disk NOT in-build disk management option. Otherwise you would be stuck with dynamic volumes which are not recognized by Drivepool and there is no way to convert them back to basic without reformatting them.

It copies it like a file, full file change, not an image backup. My understanding and observation is that if a VM is running and making changes to the virtual disk (duplication will cause errors). It happened with me, the virtualbox OS (ubuntu) started throwing errors and I'm guessing it was because of real time duplication of the VHD file. Mirror would be the safest bet. PS: I'm still recovering data from the ARQ backup.

Related to the above issue. I was copying a large VHD file and in between I got this error that the file was in use and I could skip it if needed. The file copy initiated by me was not complete yet. Then why did this happen. Shouldn't drive pool have ignored the file automatically?

Didn't have a good experience with VHD files. I was using them to mount VirtualBox virtual machines. Eventually the VHDs became RAW, and I could no longer use them. There was data loss. Also I did have a few improper shutdowns (which could have been a contributor to the problem of VHDs getting corrupted.) I have now saved the VHDs directly on the disk and not on the pool. Another thing to note, duplication uses, me thinks, a simple file copy mechanism. So if you have those VHDs mounted and then you try to copy them without Volume Shadow Service, it doesn't turn out as expected. Once even one of the VMs crashed and started throwing errors. However if those VHDs are not mounted, it is a different scenario and they are just like any other large files.

For example realtime parity!

Similar error I have as well. I try to attach RAMDisk created for cache purpose. It stays at 95% for a while eventually I get a notification that its added. However it never shows in the Pool and then when I try to add it again, I get the same error as above.

No they are not recognized. Dynamic Disks made from Disk Management are not recognized. You can use storage space and that would be recognized if you want to go that way.