Soft updates dramatically improve the performance of UFS filesystems. The newfs(8) utility currently does not enable them by default. The FreeBSD installer enables soft updates by default. However custom built installations that do not specify the -U option to newfs(8) and the prebuilt UFS system images get filesystems without soft updates enabled.
There are several testing sites that run benchmarks comparing the performance of Linux distributions versus BSD distributions. When they run filesystem comparison benchmarks they use newfs(8) to create the UFS filesystem. Because it does not have soft updates enabled it runs poorly versus the Linux ext4 filesystem. When I have suggested to them that they should enable soft updates on the UFS filesystem in their testing their response is that they expect the utility that creates the filesystem to use optimal defaults and that they cannot be expected to fiddle with various option settings.
The purpose of this change is to give a filesystem created with newfs(8) reasonably optimal settings. For UFS2 this means enabling soft updates. For UFS1 which tends to be used on small systems with minimal memory and CPU speed, the lower memory footprint of running without soft updates is a more sensible default.
This change adds a note in the section of the newfs(8) manual page that describes the -U option for enabling soft updates that they are enabled by default for UFS2 filesystems and that they can be disabled by using tunefs(8).