ZFSv28+NFSv4 poor file creation performance, "sync=disabled" has no effect

[David Brodbeck]

I'm testing FreeBSD 9.0-BETA with an eye toward eventually using
FreeBSD 9.0 to replace some existing OpenSolaris 2008.11
installations.  I've found NFS file creation performance (as measured
by Bonnie++) is equally slow for both with default settings.  However,
on OpenSolaris I disable the ZIL to improve file creation performance.
 This tuning parameter was removed from FreeBSD 9.0; its replacement
is supposed to be the per-filesystem flag "sync", but setting this
flag seems to have no effect.

I did recompile the FreeBSD kernel without debugging features before
doing the tests, so I don't think this is a case of debugging code
slowing things down.

Here's the relevant data; these are all from bonnie++'s "sequential
create" benchmark.

OpenSolaris 2008.11, default settings: 58/second
OpenSolaris 2008.11, with "zil_disable=1": 1258/second

FreeBSD 9.0-BETA, default settings: 107/second
FreeBSD 9.0-BETA, with "sync=disabled": 106/second


It appears the "sync" ZFS parameter has no effect in FreeBSD.  Has
anyone else seen this?  Is there a way to improve NFS file creation
performance now that zil_disable has been removed?