SSV-24185: Fix the number of zvol I/O threads to align with 50% of th… #99
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SSV-24185
Issue: CPU stuck at 100% is related to ZFS when we use dedup & comp, never able to reproduce the issue with Compression only enable.
Issue: Recovery speeds fluctuate significantly, likely due to CPU and thread contention under heavy I/O. In ZFS, the number of threads that accept I/O from SSY is hardcoded to 32. As a result, systems with fewer CPUs or hyper-threads may end up overusing resources.
Fix: The number of zvol I/O threads to align with 50% of the maximum available logical CPUs if the 'zvol_io_threads' value in 'Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ZFSin' is not specified. If the 'zvol_io_threads' value is provided, use this value for creating the zvol task queue thread pool.
Use kstat.exe zfs:0:tunable to check the current value of zvol_io_threads. This can be set only by updating the registry, and also require a reboot.