[How to stop wrting to a disk?]

This may be a stupid question ,but is there a way to tell unraid to stop writing to a particular disk at a certain percent full, or free space remaining?  I've seen the threads about rebalancing drives, and about guidelines for filling a disk to like 95% or 98%, and I know about the disk threshold settings for warning and critical alerts.   But I don't see a clear way to tell the server to stop writing to the disk.

[Process shfs at 100% with high io use]

I'm having similar issues when I run Docker on unraid 6.3.5.  Shfs is 100% cpu and the only solution is a hard reboot which triggers an 8-hour parity check.  I've had 3 of these in the last 4 days.