Improvements include enhancements to the way that we do logging. In vSAN, every I/O operation is logged before being processed. We have now made logging much more efficient in this update. We also improve the way large file deletes are handled. Since the I/Os involved in processing the delete operations are also logged, this can make the log can grow very large, very quickly depending on the size of the file being deleted. Preemptive destaging of data, along with the improvements to the logging mechanism, now make the delete process much more performant. This is especially noticeable when data services such as deduplication and compression are enabled. Finally, this update to vSAN has several enhancements that makes the checksum code path more efficient.
There are a number of additional improvements unrelated to performance. You can find them in the vSAN section of the release notes.