I've noticed every single time I reboot, the whole pool remeasures every disk, which takes ~3 hours to complete. During this time, the pool is borderline unusable. Launching a Steam game installed to the pool may take 5 minutes or more to launch, and then stutter for a few seconds every 5 seconds or so (completely I/O starved). Even video playback can stutter, it seems the pool just has no leftover I/O to serve requests over the measuring.
I understand that measuring has a high impact, but it doesn't seem like it should be this bad. It seems like outside I/O should have priority over the measuring.
Secondly, I understand the pool shouldn't need to remeasure every reboot. Any way to troubleshoot why this is happening? It makes the machine pretty much unusable for hours after rebooting, which I need to do periodically for updates etc.
The one thing I have which is a little unusual is the pool is all made of REFS disks. Is this possibly the culprit? Obviously moving back to NTFS would be quite an undertaking, though with Microsoft trying to drop support from the desktop versions of Win 10 it's certainly something I'm open to.
Disks in the pool are:
1x8TB WD Red
2x4TB WD Red
1x4TB WD Black
EDIT: forgot to add that when the measuring is finished, the performance settles down and becomes pretty reasonable, comparable to a normal disk. So I've been trying to avoid reboots as much as possible not to have to render the machine unusable for hours at a time.
I've also completely disabled the Windows Search Service (indexing), as I have no need for it and know it can cause performance impacts.