Comment by Almondsetat
2 days ago
OpenSSH is from the people at OpenBSD, which means performance improvements have to be carefully vetted against bugs, and, judging by the fact that they're still on fastfs and the lack of TRIM in 2025, that will not happen.
There's nothing inherently slow about UFS2; the theoretical performance profile should be nearly identical to Ext4. For basic filesystem operations UFS2 and Ext4 will often be faster than more modern filesystems.
OpenBSD's filesystem operations are slow not because of UFS2, but because they simply haven't been optimized up-and-down the stack the way Ext4 has been Linux or UFS2 on FreeBSD. And of course, OpenBSD's implementation doesn't have a journal (both UFS and Ext had journaling bolted late in life) so filesystem checks (triggered on an unclean shutdown or after N boots) can take a long time, which often cause people to think their system has frozen or didn't come up. That user interface problem notwithstanding, UFS2 is extremely robust. OpenBSD is very conservative about optimizations, especially when they increase code complexity, and particularly for subsystems where the project doesn't have time available to give it the necessary attention.
OpenBSD UFS did have "soft updates" which were some kind of alternative to journaling.
I believe that these were recently removed. Perhaps they don't play well with SMP.
McKusick, who wrote the original BSD FFS, also later came up with SU:
* https://en.wikipedia.org/wiki/Soft_updates