> noticed some drawbacks, such as when (for example) untarring pkgsrc. If I'm
> doing it on a softdep'd partition on a nice fast disk (this box is an
> XP2700+ with 1GB ram) it'll complete in about 19 seconds - then lag the HELL
> out of the machine as it actually goes about doing the real writes. To the
> point where it almost feels like it's hardlocked the system. I've had this
> happen several times, only on softdep'd filesystems.

It'll happen on async'd filesystems too.  :)  I do this on purpose when
extracting pkgsrc. My /usr/pkgsrc lives on a fs I use only for unmodified
distributed file sets so if the worst happens it's easy to repopulate
(a writable fs union-mounts above it).  Before extracting a new pkgsrc,
I remount the dist fs async.  The extract goes super fast, then the machine
quietly writes for another minute or two at the end.  Then I type 'sync'
and it quietly writes for another minute or so.  :)  Then I remount the fs
noasync and go on my way.

For me the lag at the end is a Good Thing.  For one thing, the total time for
the extract plus two or three minutes of writing back at the end is SO much
less than it would be noasync.  The other thing is the disk is doing almost
all sequential writing - that's why it's so quiet it almost seems like the
machine's hung - it's not sounding like an old movie projector, bouncing the
rw head violently all over the disk and taking that much toll on the drive.
My hard drive thanks me for it.

-Chap