SQL Server 2017 leverages up to 4 log writer workers, on hidden schedulers, to assist in transaction log processing activities. You may find the number of log write workers has been increased to 8 when running newer releases of SQL Server to accommodate larger systems. (Caution: Pre-release software may change before final release.)
During SQL Server startup the number of log writer workers is determined.
If multiple log write workers are not allowed use a single log writer
- Total number NUMA nodes * 2
- Count the number of available CPUs on the NUMA node (affinity mask can impact this count)
Take the smaller of the above calculations and cap by the MAX_LOG_WRITERS allowed (4 or 8 depending on version)