S-U brings considerable benefits akin to JFS for crash protection to *BSD
systems. Essentially, they are ordered disk writes that makes sure data
gets on the disk before metadata is altered. They go through the buffering
system, so performance isn't bad.
As an experiment, I pulled the plug towards the end of 5 FreeBSD kernel
compiles (SMP `make -j4`). In all cases, the fsck upon restart was minor,
just freeing inodes. In four of the cases, `make` just picked up where
it left off, and finished the kernel compile, losing only ~40 seconds work!
In one case, a `make clean` had to be done because something was incomplete.
You boys and girls don't try this at home on Linux! The ext2 fsck is horrible
after a powerfail, and I've lost superblocks and had to re-install :( .
-- Robert
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