According to the support team, it seems that CBT will not work with ReFS volumes on Windows 10. The whole volume must be read for each incremental. They said that because of the slow IO on one of the drives in the Storage Pool the ReFS can't use CBT. I've asked some questions of them and I'm waiting to hear back. I would be interested if anyone has successfully used CBT for any ReFS volume, be it directly on a single physical disk or storage pool. I'll post their statement along with my questions below. I'll also post their response to these questions when I receive it.
Suport Team statement:
"We have heard back from research and testing. They have found that while Windows 10 storage spaces will work, the average processing read/write speed was lower than that of the read/write speed of the slowest disk during tests. The extra time it takes to read 3TB appears to be expected behavior for a Windows 10 storage spaces setup.
Let me know if you have any further questions."
My follow up questions:
"I guess I'm confused and could use some clarification. VAW is supposed to support CBT on ReFS volumes, but because of the I/O deficiency of the physical disks in the storage pool it won't work in Windows 10? How does VAW even interact with the physical disks directly when it is presented with a virtual disk by Windows? Would CBT work on the ReFS volume if I was running Windows Server 2016 instead? And why does CBT work on a NTFS volume in the same storage pool if the pool itself is the problem? Any clarification would be greatly appreciated."
Just to be clear, I think the Veeam Support Team has done a great job troubleshooting this issue so far. They are professional and quick to respond. If it turns out that ReFS volumes just don't support CBT, then maybe that is something that can be addressed in the next release. I'm sure many users aren't running production ReFS volumes, but it will be more common as time goes on considering the features the file system offers.